Neutralizing Antibody Research Articles

Neutralizing antibody responses to three XBB protein vaccines in older adults

The ongoing COVID-19 pandemic has underscored the importance of strong immune defenses against emerging SARS-CoV-2 variants. While COVID-19 vaccines containing XBB subvariants have proven effective in neutralizing new SARS-CoV-2 variants, a gap remains in knowledge regarding neutralizing antibody responses in older adults aged >65 years against these newly emerged variants. This study was therefore undertaken to investigate and compare neutralizing antibody responses to three XBB-containing protein-based vaccines (trivalent XBB.1.5 vaccine, bivalent Omicron XBB vaccine, and tetravalent XBB.1 vaccine) head-to-head in 90 individuals aged >65 years. The results showed that all three XBB-containing vaccines substantially enhanced the neutralizing antibody response, with 100% of vaccinees having detectable antibody titers against ancestral D614G and variants BA.5, XBB.1.5, JN.1, KP.2, and KP.3 after booster immunization. Subsequent analysis indicated that the trivalent XBB.1.5 and tetravalent XBB.1 vaccines elicited higher levels of neutralizing antibodies compared to the bivalent Omicron XBB vaccine. The KP.2 and KP.3 variants displayed antibody resistance comparable to the JN.1 variant. Older adults produce similar neutralizing antibody responses to the vaccines regardless of their underlying medical conditions. These findings indicate that booster vaccination with XBB-containing vaccines can effectively elicit strong neutralizing responses against a number of SARS-CoV-2 variants in older adults over 65 years, which will help guide vaccine strategies in this elderly population.

Atezolizumab neutralizing assay development: a novel way of evaluating assay cutpoint after sample pretreatment

Atezolizumab, a biotherapeutic monoclonal antibody directed against PD-L1, has been shown to be efficacious in multiple oncology indications. In clinical trials, a subset of patients developed anti-atezolizumab antibodies, necessitating the development of a neutralizing antibody (NAb) assay. A bead-based sample pretreatment method was developed to reduce high levels of therapeutic in patient serum samples. Untreated sample variability is reduced by this sample pretreatment, based on this, a novel approach was taken for determining an appropriate assay decision threshold (cutpoint). The therapeutic was added to the samples to mimic typical patient samples. The resulting assay was successfully validated and applied to sample analysis from multiple clinical trials.

Antibody responses in omicron BF.7-infected patients vaccinated with inactivated SARS-CoV-2.

Our study aimed to investigate antibody responses in omicron BF.7-infected patients after being vaccinated with inactivated SARS-CoV-2. Blood serum samples were collected every 2-7d, 1 w before infection, during the acute infection period and recovery period, and every month after recovery to detect IgG, IgM, IgA, neutralizing antibodies, and neutralizing antibodies against different omicrons in the acute phase. The levels of IgG, IgA and neutralizing antibodies increased sharply at 6-7d after infection, and the levels of IgG and neutralizing antibodies peaked rapidly within 1-2 w, lasting for 3-4 w, and the antibody levels gradually decreased at 4-8 w after infection. The level of neutralizing antibodies against the wild-type strain SARS-CoV-2 was much greater than that against the variant strains during the acute infection period. After being infected with omicron BF.7, the IgG and neutralizing antibodies in inactivated SARS-CoV-2-vaccinated individuals increase sharply 6-7 days after infection, which is earlier than those in the initial WT SARS-CoV-2 infection, and the peak time within 1-2 w is shorter. The levels of IgG, neutralizing antibody, and IgA antibodies are high, and the levels of IgM antibodies are low; however, the neutralizing antibodies are mainly against the wild-type strain of SARS-CoV-2.

Development and immunogenicity evaluation of attenuated Salmonella typhimurium delivering porcine Deltacoronavirus S1 gene.

Porcine deltacoronavirus (PDCoV) is a swine enteropathogenic coronavirus that causes severe diarrhea in piglets, the development of novel vaccines is of great value in the prevention and control of PDCoV. Here, we selected attenuated Salmonella typhimurium SL7207 to deliver pVAX1-S1, resulting in the oral vaccine strain, SL7207 (pVAX1-S1). In immunized mice, SL7207 (pVAX1-S1) induced PDCoV-specific humoral IgG, IgA, neutralizing antibodies, mucosal sIgA, up-regulation of CD8+ T cells, and increased levels of Th1 cytokines (IFN-γ and IL-2). In piglets, SL7207 (pVAX1-S1) induced high levels of PDCoV-specific humoral IgG and neutralizing antibodies but no detectable IgA, and only low levels of mucosal sIgA. SL7207 (pVAX1-S1) also promoted T cell differentiation into CD4+ and CD8+ T cells, and increased the expression level of IFN-γ and IL-4 in peripheral blood. Challenge experiments in piglets showed SL7207 (pVAX1-S1) alleviated diarrhea, decreased fecal virus load and intestinal lesions compared with control groups. In conclusion, this study systematically evaluated the immunogenicity and feasibility of attenuated Salmonella typhimurium delivering PDCoV S1 gene, which will provide helpful reference information for further exploration of novel PDCoV oral vaccine.

Immunogenicity of yellow fever vaccine co-administered with 13-valent pneumococcal conjugate vaccine in rural Gambia: A cluster-randomised trial.

Because booster doses of pneumococcal conjugate vaccine (PCV) may be given at a similar time to yellow fever vaccine (YF), it is important to assess the immune response to YF when co-administered with PCV. This has been investigated during a reduced-dose PCV trial in The Gambia. In this phase 4, parallel-group, cluster-randomized trial, healthy infants aged 0-10weeks were randomly allocated to receive either a two-dose schedule of PCV13 with a booster dose co-administered with YF vaccine at age 9months (1+1 co-administration) or YF vaccine administered separately at age 10months (1+1 separate) or the standard three early doses of PCV13 with YF vaccine at age 9months (3+0 separate). Blood samples were collected 28-35days post-vaccination and YF neutralizing antibody (NA) titres were measured. Proportions with seroprotective YF NA titres≥1:8 were calculated with 95% confidence intervals (CI). Non-inferiority was demonstrated if the lower limit of the CI for the difference in proportions between the co-administration and separate groups was greater than-10%. Forty-eight, 66, and 98 participants enrolled in 3+0 separate, 1+1 co-administration, and 1+1 separate groups respectively had NA results. Per protocol analysis of the 3+0 separate, 1+1 co-administration, 1+1 separate, and the combined 1+1 separate and 3+0 separate groups found that 81%, 85%, 92%, and 88% of participants respectively had YF NA titres ≥1:8. Results were similar with analysis by intention-to-treat. The difference in proportions comparing 1+1 co-administration and 1+1 separate groups was -7% (95% CI, -18% to 3%). The difference between 1+1 co-administration and 3+0 separate groups was 4% (95% CI, -10% to 15%). There was no statistical difference in the YF seroresponse when the YF vaccine was co-administered with PCV or administered separately. No evidence was found of the non-inferiority of the seroresponse to YF vaccine when co-administered with PCV13. The levels of YF NA attaining seroprotection (NT ≥1:8) were high in all groups. PCV13 co-administered with YF vaccine at 9months does not affect seroresponse to YF vaccine. http://www.isrctn.org/ - ISRCTN72821613.

Assessing Torquetenovirus (TTV) as a Biomarker for Immune Responses to SARS-CoV-2 mRNA Vaccines in People Living with HIV and Healthy Individuals

Background: Torquetenovirus (TTV) viremia is increasingly recognized as a marker of immune competence. In the context of COVID-19, TTV viral load (VL) has been shown to predict anti-Spike antibody levels in severely immunocompromised patients. This study aimed to evaluate whether pre-vaccine TTV VL could predict humoral and cellular immune responses to SARS-CoV-2 mRNA vaccines in people living with HIV (PLWH) and healthy individuals (HP). Methods: TTV VL was measured via real-time PCR in serum samples collected before the second and third doses of mRNA vaccines in 93 PLWH and 48 HP (second dose) and 255 PLWH and 48 HP (third dose). Immune responses were assessed through anti-SARS-CoV-2 receptor-binding domain (RBD) IgG, neutralizing antibodies, and IFN-γ release. Statistical analyses included correlation studies between TTV VL and vaccine-induced immune responses. Results: TTV VL did not significantly correlate with anti-RBD IgG or neutralizing antibody levels in either cohort; highlighting its limited predictive value for humoral responses in relatively immunocompetent populations. However, a strong inverse correlation was observed between TTV VL and IFN-γ release after the third, but not the second, vaccine dose. These findings suggest that higher TTV VL, indicative of reduced immune competence, may impair T-cell-mediated immunity to vaccines. Conclusions: In virologically suppressed PLWH and HP, TTV VL is not a reliable predictor of humoral immune responses to COVID-19 vaccines. However, its inverse relationship with cellular responses warrants further investigation in more immunosuppressed populations. These results reinforce the continuum model of TTV VL as a biomarker, with predictive utility increasing alongside the degree of immunosuppression

Effectiveness and Immunogenicity of the MMR Vaccine Against SARS-CoV-2 Among Healthcare Workers

The purpose of this study was to evaluate the effectiveness and immunogenicity of the measles–mumps–rubella (MMR) vaccine against SARS-CoV-2 in healthcare workers at one medical institution. The effectiveness of the MMR vaccine against SARS-CoV-2 was evaluated in overall healthcare workers (HCWs). In addition, neutralizing antibodies to SARS-CoV-2 were measured according to the subjects’ measles immunity status with serum samples collected before the coronavirus disease 2019 pandemic period. The effectiveness of the MMR vaccine for SARS-CoV-2 in all HCWs and measles IgG-positive subjects was 34% (adjusted odds ratio [aOR] = 1.20, 95% confidence interval [CI] = 0.53–2.70) and 34% (aOR = 0.66, CI = 0.38–18.4), respectively. The neutralizing antibody levels for SARS-CoV-2 were low in all groups regardless of the measles immune status. The MMR vaccine alone may not provide sufficient protection against SARS-CoV-2.

Comparison of neuraminidase inhibiting antibody responses elicited by egg- and cell-derived influenza vaccines.

An immunogenicity sub-study was performed within a clinical trial comparing the effectiveness of egg, cell, and recombinant hemagglutinin (HA)-derived influenza vaccines during the 2018-2019 and 2019-2020 influenza seasons. NAI and neutralizing antibody titers against the A(H1N1)pdm09 and A(H3N2) components of the vaccines were measured in pre- and post-vaccination sera. Responses to the N1 component of eIIV and cIIV were different in both study years 1 and 2 whereas response rate and antibody titers to the N2 component of egg and cell culture-derived vaccines were similar. For example, 43.5% of eIIV and no cIIV recipients had four-fold NAI titer increases in year 1. There was a weak positive correlation between responses to N1 and N2 for both vaccine types but no correlation between NAI and HA-specific neutralizing antibody responses. Recombinant HA vaccine that does not contain NA served as a specificity control; NAI antibody titers did not increase in recipients except in two individuals presumed to have subclinical infection. Antibody responses to NA following vaccination with eIIV and cIIV were not the same; although the responses to the N1 and N2 components of eIIV were similar, there were fewer responders to N1 than N2 of cIIV. Studies to determine the impact of NA immunity on influenza vaccine effectiveness are warranted.

Safety and immunogenicity of different 17DD yellow fever vaccines in golden-headed tamarins (Leontopithecus chrysomelas): Inhibition of viremia and RNAemia after homologous live-attenuated vaccination.

Yellow fever (YF) is a viral disease that affects both humans and non-human primates (NHPs). Neotropical monkeys are more severely stricken by YF and the impact of the disease can be devastating to the endangered golden-headed lion tamarins (GHLTs, Leontopithecus chrysomelas). Susceptible GHLTs were immunized with the commercial Brazilian YF 17DD live attenuated vaccine or two other experimental non-replicating YF vaccines: a purified whole-virus, b-propiolactone-inactivated vaccine and a plant-derived recombinant subunit vaccine. Safety, immunogenicity and viremia and RNAemia blockade were characterized. No YF clinical manifestations were observed in any of the GHLTs that received the attenuated virus, either as a vaccine or as the homologous vaccination with the live attenuated vaccine used as the challenge virus. All three concentrations of the attenuated vaccine induced neutralizing antibodies and only one in 16 animals had detectable viremia and RNAemia after challenge. The inactivated vaccine elicited neutralizing antibodies preventing post-challenge viremia and RNAemia in five out of six animals. The plant-based vaccine induced neutralizing antibodies in five out of six animals and prevented viremia and RNAemia in three out of six against challenge. The safety profile and the immunogenicity of the YF attenuated vaccine were demonstrated in GHLTs with a blocking effectiveness over 90%, where blockade can be defined as the capacity to prevent viremia and RNAemia after homologous vaccination with the live attenuated vaccine. The use of the inactivated vaccine in this species served as a preliminary pre-clinical study for this approach and after administration in three-dose regimen demonstrated a blocking profile of 83%. Using a two-dose regimen, the plant-based vaccine was able to block viremia and RNAemia in 50% of the animals. The present study can endorse the use of attenuated or non-replicating yellow fever vaccines in New World primates threatened by the recent disease outbreaks in Brazil.

Development and Efficacy Evaluation of a Novel Nanoparticle-Based Hemagglutination Inhibition Assay for Serological Studies of Porcine Epidemic Diarrhea Virus

Porcine epidemic diarrhea virus (PEDV) is a major pathogen that causes serious economic losses to the swine industry. To aid PEDV clinical diagnosis and vaccine development, sensitive and precise serological methods are demanded for rapid detection of (neutralizing) antibodies. Aiming for the development of a novel virus-free hemagglutination inhibition (HI) assay, the N-terminal region of the PEDV S1 subunit, encompassing the sialic acid-binding motif, was first expressed as an Fc-fusion protein with a C-terminal Spy Tag (S10A-Spy). The S10A-Spy protein was then presented on SpyCatcher-mi3 nanoparticles, forming virus-like particles designated S10A-NPs. Electron microscopy and dynamic light scattering analysis confirmed its topology, and the hemagglutination assay showed that S10A-NPs can efficiently agglutinate red blood cells. The HI assay based on S10A-NPs was then validated with PEDV-positive and -negative samples. The results showed that the HI assay had high specificity for the detection of PEDV antibodies. Next, a total of 253 clinical serum samples were subjected to the HI testing along with virus neutralization (VN) assay. The area under the receiver operating characteristic curve with VN was 0.959, and the kappa value was 0.759. Statistical analysis of the results indicated that the HI titers of the samples tested exhibited high consistency with the VN titers. Taken together, a novel virus-free HI assay based on the multivalent display of a chimeric PEDV spike protein upon self-assembling nanoparticles was established, providing a new approach for PEDV serological diagnosis.

Effect of vaccination against foot-and-mouth disease during mid-pregnancy on the neutralizing antibody response in the cow.

As pregnancy can adversely affect the immune response of vaccination against foot and mouth disease virus (FMDV) due to physiological immunosuppressive milieu, we tested the effect of FMDV vaccination during mid-gestation on the antibody response. Pregnant and non-pregnant cows of crossbred and indigenous breed (n=28/group) were vaccinated with inactivated FMD vaccine covering O, A, and Asia1 serotypes and the sera were harvested at weekly interval till day 42 post-vaccination. Virus neutralization test (VNT) was done and the analysis of log10 VN50 antibody titer by mixed model ANOVA indicated that pregnancy did not significantly affect the log10 VN50 titer for FMDV serotype O and Asia1. Though pregnancy significantly decreased the titer for FMDV serotype A, the effect size was small. The experiment was repeated in purebred HF cows (n=10/group) and the results were reproducible. It was concluded that mid-pregnancy would not hamper the herd immunity to FMD vaccination in the cow.

Development and Immunogenicity Study of Subunit Vaccines Based on Spike Proteins of Porcine Epidemic Diarrhea Virus and Porcine Transmissible Gastroenteritis Virus

Porcine epidemic diarrhea virus (PEDV) and transmissible gastroenteritis virus (TGEV) are responsible for significant economic losses in the swine industry. The S1 proteins of these viruses serve as key targets for vaccine development. In this study, prokaryotic expression vectors for pCZN1-PEDV S1, pCZN1-TGEV S1, and pCZN1-PEDV S1-TGEV S1 were constructed. The corresponding proteins were expressed, purified, and used to prepare monovalent, bivalent, and mixed (PEDV S1 + TGEV S1) vaccines. Kunming (KM) mice were immunized with subunit vaccines, with PBS as the negative control (NC) and a commercial inactivated vaccine as the positive control (PC). Immune responses, including specific antibody (IgG, IgG1, IgG2a) levels, virus neutralization, and IFN-γ production, were evaluated. All vaccines induced high levels of specific IgG, IgG1, and IgG2a antibodies. At weeks 2 and 8, the PEDV S1 + TGEV S1 vaccine induced significantly higher levels of specific IgG and IgG1 compared to the PC (p < 0.001). The PEDV S1 vaccine also induced significantly higher specific IgG2a levels than the PC at week 4 (p < 0.0001). Virus neutralization assays demonstrated that the subunit vaccines induced neutralizing antibody levels comparable to or exceeding those of the PC. Furthermore, IFN-γ levels were significantly elevated in all vaccinated groups compared to the NC (p < 0.0001), indicating a robust immune response. These results suggest that the subunit vaccines are promising candidates for the safe and effective control of both PEDV and TGEV infections.

Humoral and cellular immune responses after 6months of a heterologous SARS-CoV-2 booster with the protein-based PHH-1V vaccine in a phase IIb trial.

The HIPRA-HH-2 was a multicentre, randomized, active-controlled, double-blind, non-inferiority phase IIb clinical trial comparing the immunogenicity and safety of the PHH-1V adjuvanted recombinant vaccine as a heterologous booster against homologous booster with BNT162b2. Interim results demonstrated strong humoral and cellular immune response against the SARS-CoV-2 Wuhan-Hu-1 strain and the Beta, Delta, and Omicron BA.1 variants up to day 98 post-dosing. Here we report that these responses with PHH-1V are sustained up to 6months, including in participants over 65years, despite their smaller sample size. The PHH-1V booster was non-inferior in eliciting neutralizing antibodies for SARS-CoV-2 Omicron XBB.1.5 variant compared to BNT162b2 after 6months. No severe COVID-19 cases occurred in any group, and mild cases were similar (50.4% for PHH-1V vs. 47.8% for BNT162b2). While both groups may have reached comparable immunity levels, these findings suggest that the PHH-1V vaccine provides long-lasting immunity against various of SARS-CoV-2 variants. ClinicalTrials.gov Identifier: NCT05142553.

A third COVID-19 vaccine dose in kidney transplant recipients induces antibody response to vaccine and Omicron variants but shows limited Ig subclass switching.

Solid organ transplant recipients (SOTRs) suffer more frequent and more severe infections due to their compromised immune responses resulting from immunosuppressive treatments designed to prevent organ rejection. Pharmacological immunosuppression can adversely affect immune responses to vaccination. A cohort of kidney transplant recipients (KTRs) received their third dose of ancestral, monovalent COVID-19 vaccine in the context of a clinical trial and antibody responses to the vaccine strain, as well as two Omicron variants BA.1 and BA.5 were investigated and compared with healthy controls who also received a third dose of mRNA vaccine (HCs). Total IgG and live virus neutralizing antibody titers were reduced in KTRs compared with controls for all variants. KTRs displayed altered IgG subclass switching, with significantly lower IgG3 antibodies. Responses in KTRs were also very heterogeneous, with some individuals showing strong responses but a significant number showing no Omicron-specific neutralizing antibodies. Taken together, immune responses after COVID-19 vaccination in KTRs were not only lower than HCs but highly variable, indicating that simply increasing the number of vaccine doses alone may not be sufficient to provide greater protection in this population. These findings underscore the need for tailored vaccination strategies for immunosuppressed populations, such as KTRs. Alternative formulations and doses of COVID-19 vaccines should be considered for people with severely compromised immune systems, as more frequent vaccinations may not significantly improve the response, especially regarding neutralizing antibodies.IMPORTANCEThis study addresses the challenges faced by kidney transplant recipients (KTRs) in mounting effective immune responses against COVID-19. By evaluating the antibody responses to a third dose of monovalent mRNA COVID-19 vaccine and its effectiveness against Omicron subvariants (BA.1 and BA.5), this study reveals significant reductions in both binding and neutralizing antibodies in KTRs compared with healthy controls. The research highlights altered IgG subclass switching and heterogeneous responses within the KTR population. Reduced recognition of variants, coupled with differences in IgG subclasses, decreases both the quality and quantity of protective antibodies after vaccination in KTRs. These findings underscore the need for tailored vaccination strategies for immunosuppressed populations, such as KTRs. Alternative formulations and doses of COVID-19 vaccines should be considered for people with severely compromised immune systems, as more frequent vaccinations may not significantly improve the response, especially regarding neutralizing antibodies.

Short-term evolution of Mpox-specific IgG and neutralizing antibodies among individuals undergoing MVA-BN vaccination.

The data on immune responses of individuals undergoing MVA-BN vaccination are scarce. We aimed to compare Mpox virus-specific antibody and neutralizing antibody responses among people with and without HIV receiving MVA-BN vaccines. This prospective study enrolled participants undergoing two-dose MVA-BN vaccination to investigate seroresponses after vaccination. Blood samples were collected before and after each dose of vaccination for determinations of anti-A29 and anti-H3 IgG. Neutralization tests were conducted for samples tested positive for both anti-A29 and anti-H3 IgG. Overall, 441 participants undergoing two-dose MVA-BN vaccination were enrolled. Seroconversion for anti-A29 and anti-H3 IgG, respectively, after the second dose of vaccination was 18.2% and 61.2%, 10.9% and 65.0%, and 51.6% and 90.6% among PWH, PWoH, and those who had had smallpox vaccination previously, respectively. About 20% of the participants with seroconversion lost seroresponses after a 7-month period of observation. None of the serum samples from vaccinated participants demonstrated neutralizing ability. Participants with previous smallpox vaccination had higher and more sustained antibody responses after receiving two doses of MVA-BN vaccines than those who had not undergone smallpox vaccination. More studies are warranted to assess the seroresponses to booster MVA-BN vaccination for vaccine non-responders or those having lost seroresponses.

Human proximal tubular epithelial cell interleukin-1 receptor signalling triggers G2/M arrest and cellular senescence during hypoxic kidney injury

Hypoxia and interleukin (IL)-1β are independent mediators of tubulointerstitial fibrosis, the histological hallmark of chronic kidney disease (CKD). Here, we examine how hypoxia and IL-1β act in synergy to augment maladaptive proximal tubular epithelial cell (PTEC) repair in human CKD. Ex vivo patient-derived PTECs were cultured under normoxic (21% O2) or hypoxic (1% O2) conditions in the absence or presence of IL-1β and examined for maladaptive repair signatures. Hypoxic PTECs incubated with IL-1β displayed a discrete transcriptomic profile distinct from PTECs cultured under hypoxia alone, IL-1β alone or under normoxia. Hypoxia+IL-1β-treated PTECs had 692 ‘unique’ differentially expressed genes (DEGs) compared to normoxic PTECs, with ‘cell cycle’ the most significantly enriched KEGG pathway based on ‘unique’ down-regulated DEGs (including CCNA2, CCNB1 and CCNB2). Hypoxia+IL-1β-treated PTECs displayed signatures of cellular senescence, with reduced proliferation, G2/M cell cycle arrest, increased p21 expression, elevated senescence-associated β-galactosidase (SA-β-gal) activity and increased production of pro-inflammatory/fibrotic senescence-associated secretory phenotype (SASP) factors compared to normoxic conditions. Treatment of Hypoxia+IL-1β-treated PTECs with either a type I IL-1 receptor (IL-1RI) neutralizing antibody or a senolytic drug combination, quercetin+dasatinib, attenuated senescent cell burden. In vitro findings were validated in human CKD bio-specimens (kidney tissue, urine), with elevated PTEC IL-1RI expression and senescence (SA-β-gal activity) detected in fibrotic kidneys and numbers of senescent (SA-β-gal+) urinary PTECs correlating with urinary IL-1β levels and severity of interstitial fibrosis. Our data identify a mechanism whereby hypoxia in combination with IL-1β/IL-1RI signalling trigger PTEC senescence, providing novel therapeutic and diagnostic check-points for restoring tubular regeneration in human CKD.

A-910823, a squalene-based emulsion adjuvant, enhances robust and broad immune responses of quadrivalent influenza vaccine in ferrets.

Robust and broad protective immunity is typically elicited by co-administration of an adjuvant with vaccine antigens. A-910823, a squalene-based emulsion adjuvant, has been approved in Japan. It effectively enhances the humoral and cellular immunity of S-268019-b, a recombinant COVID-19 vaccine; however, the adjuvant effects of A-910823 on other vaccines, including influenza vaccine, have not been evaluated. Here, a ferret model was employed to investigate the adjuvant effects of A-910823 when combined with split-inactivated quadrivalent influenza vaccine (QIV). We demonstrate that combination of A-910823 with QIV enhances the neutralizing antibody titer and its breadth against non-vaccine strains. Also, the protective efficacy of A-910823-adjuvanted QIV against virus challenge has been confirmed. Of note, QIV combined with A-910823 caused only minor detectable side effects, whereas a significant increase in fever was observed after two doses of mRNA-LNP in ferrets. This study provides information on the effectiveness and safety of A-910823-adjuvanted QIV and suggests the usefulness of the ferret model for evaluating vaccine-induced reactogenicity.

Monocytes and interstitial macrophages contribute to hypoxic pulmonary hypertension.

Hypoxia is a major cause of pulmonary hypertension (PH) worldwide, and it is likely that interstitial pulmonary macrophages contribute to this vascular pathology. We observed in hypoxia-exposed mice an increase in resident interstitial macrophages, which expanded through proliferation and expressed the monocyte recruitment ligand CCL2. We also observed an increase in CCR2+ macrophages through recruitment, which express the protein thrombospondin-1 that functionally activates TGF-beta to cause vascular disease. Blockade of monocyte recruitment with either CCL2 neutralizing antibody treatment or CCR2 deficiency in the bone marrow compartment suppressed hypoxic PH. These data were supported by analysis of plasma samples from humans who travelled from low (225m) to high (3500m) elevation, revealing an increase in thrombospondin-1 and TGF-beta expression following ascent, which was blocked by dexamethasone prophylaxis. In the hypoxic mouse model, dexamethasone prophylaxis recapitulated these findings by mechanistically suppressing CCL2 expression and CCR2+ monocyte recruitment. These data suggest a pathologic cross-talk between two discrete interstitial macrophage populations, which can be therapeutically targeted.

P-2063. Safety and Immunogenicity of Booster Vaccination Against COVID-19 with Whole-SARS-CoV-2-Virion Inactivated Vaccine KD-414: A Phase 1 Trial in Japan

Abstract Background SARS-CoV-2 mRNA vaccines induce effective immunity, but wane over time. With COVID-19 now endemic, there is a growing population with hybrid immunity. Booster immunization with a vaccine that offers fewer adverse events and sustained immunity is imperative. Methods We conducted an open-label, dose-fixed, multi-group, single-center study for adults (≥20 years old) in Japan, administering a single booster dose of KD-414, a whole-SARS-CoV-2-virion inactivated vaccine, after primary vaccination with mRNA vaccines (BNT162b2, mRNA-1273), including post-SARS-CoV-2 infection (jRCT1031210517). Safety and immunogenicity were assessed using the geometric mean titer (GMT) of serum neutralizing antibodies (NA) against the vaccine strain [Wuhan strain (W)], and an Omicron strain (BA1). T-cell function in peripheral blood mononuclear cells (PBMCs) was also evaluated after stimulation with SARS-CoV-2-S, M, and N peptide vaccine strains using a multiplex system. Subjects were observed for 52 weeks if they remained uninfected with SARS-CoV-2 and did not receive additional vaccinations. Results Among the 102 adult volunteers enrolled (Figure 1), KD-414 was well tolerated, with vaccine-specific adverse events predominantly grade 1 (Figure 2). The GMT of W strain NA before booster injection varied, resulting in categorization into low, medium, and high groups based on NA. The proportion of subjects with at least a 4-fold increase in NA in the low group increased to 54.5% (18/33) at 4 weeks (Figure 3). IFN-γrelease by PBMCs stimulated with each peptide correlated with W strain NA (Figure 3). The proportion of subjects with NA upregulation of 10 or more in the medium and high groups remained at 100% until 52 weeks, whereas the low group showed a decrease to 92.3% and 66.7% at 26 weeks and 52 weeks, respectively (Figure 4). Regarding the GMT of BA1 strain NA, previously infected subjects exhibited higher levels (data not shown). The proportion of subjects with NA upregulation of 10 or more in the medium and high groups also remained at 100% until 52 weeks (Figure 4). Conclusion A single booster dose of KD-414 showed good tolerability and immunogenicity, suggesting its potential as s safe and novel SARS-CoV-2 booster vaccine for individuals with hybrid immunity. Disclosures Michiko Koga, MD,PhD, KM biologics: Grant/Research Support Masahiro Nojima, M.D.,Ph.D., KM biologics: Grant/Research Support Kengo Sonoda, PhD, KM Biologics Co., Ltd.: Kengo Sonoda is an employee of KM Biologics Co., Ltd. Ken Ishii, M.D., Ph.D., KM biologics: Grant/Research Support Yoshihiro Kawaoka, DVM, Ph.D., Daiichi Sankyo: Grant/Research Support|FluGen: Stocks/Bonds (Private Company)|KM Biologics: Grant/Research Support Fumitaka Nagamura, M.D., Ph.D, DeNA Life Science: IRB member Hiroshi Yotsuyanagi, MD PhD, Japanese Society of Infectious Disease: President|Shionogi & Co., Ltd.: Board Member|Shionogi & Co., Ltd.: Lecture fees, travel and meeting support, and Chairs in sponsored symposiums|ViiV Healthcare: Lecture fees; Chairs in sponsored symposiums

Long-Term Immune Consequences of Initial SARS-CoV-2 A.23.1 Exposure: A Longitudinal Study of Antibody Responses and Cross-Neutralization in a Ugandan Cohort

Background: This study assessed the long-term dynamics of neutralizing antibodies in a Ugandan cohort primarily exposed to the A.23.1 SARS-CoV-2 variant, examining how this shaped immune breadth and potency against diverse strains following infection and prototype-based vaccination. Methods: We conducted a 427-day retrospective analysis of 41 participants across multiple SARS-CoV-2 waves, assessing binding and neutralizing antibody responses using in-house ELISA and pseudotyped virus neutralization assays. We quantified immune responses to key SARS-CoV-2 variants, A.23.1, D614G, Delta, and BA.4, capturing evolving immunity across the pandemic. Results: Neutralizing antibody titers against A.23.1 remained significantly higher than those against D614G, Delta, and BA.4, highlighting the solid immune memory following A.23.1 infection. Consistently lower titers were observed for BA.4 across all time points, aligning with its strong immune-evasion capability. Correlations between neutralizing titers and spike-directed IgG (S-IgG) concentrations were significantly stronger for A.23.1 than for D614G, with no correlation for BA.4. ChAdOx1-S vaccination substantially elevated the neutralizing titers across all variants, most notably BA.4, highlighting the essential role of vaccination in boosting immunity, even in individuals with initially low titers. Conclusions: Initial exposure to the A.23.1 variant triggered potent immune responses, shaping neutralizing antibody dynamics during subsequent exposures. These findings highlight the importance of accounting for early viral exposures in vaccine development and public health planning. The distinctly lower immune response to BA.4 highlights the need for continuous antigenic monitoring and timely vaccine updates for protection against emerging variants. Vaccination remains essential for reinforcing and sustaining immunity against evolving variants.