Increased Neutralizing Antibody Research Articles

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

Comparison of Vaccination Regimens on Immune Responses Using PED Replicon Vaccine: A Field Trial in PED-Negative and PED-Positive Thai Swine Farms.

Porcine epidemic diarrhea virus (PEDV) is an economically important pathogen of swine, causing severe diarrhea in neonates with high morbidity and mortality. Vaccination is a key strategy for PEDV control, but optimizing regimens based on herd status is essential for improving immunity and protection. This study evaluated immune responses to different vaccination protocols using a PED replicon vaccine (PED-RP) in Thai swine farms with varying PED statuses. Two field trials were conducted: Experiment 1 (n = 120) on a PED-negative farm used a killed vaccine followed by PED-RP, while Experiment 2 (n = 42) on a PED-positive farm used a modified-live vaccine (MLV) followed by PED-RP. In Experiment 1, gilts boosted with PED-RP during gestation showed significantly higher colostrum IgA levels compared to those receiving two doses of the killed vaccine. In Experiment 2, priming with MLV followed by PED-RP resulted in increased neutralizing antibody titers and seropositivity, outperforming the MLV-only regimen after acclimatization. These findings suggest that using PED-RP as a booster can enhance serum and lactogenic immunity, providing a promising strategy for improving immune responses in both PED-negative and PED-positive herds. The study highlights the importance of tailored vaccination strategies to optimize herd immunity and protect piglets from PEDV.

An oral vaccine based on the Ad5 vector with a double-stranded RNA adjuvant protects mice against respiratory syncytial virus.

A safe and effective vaccine is urgently needed to prevent acute respiratory infections caused by respiratory syncytial virus (RSV). Oral administration offers several advantages, including ease of delivery, minimal stress for vaccine recipients, and greater safety than the systemic injection. In this study, we developed an oral vaccine candidate based on the human adenovirus serotype 5 (Ad5) vector, Ad5-PreF-DS2, encoding a prefusion protein of RSV with a dsRNA as an endogenous adjuvant. We evaluated the immunogenicity and protective efficacy of oral immunization against an RSV challenge in mice, comparing it with those of IM and IN immunizations. Subsequently, we performed an in-depth analysis of the B cell immune response to the oral vaccine. Our findings indicate that oral vaccines elicited a robust antibody response, T-cell response, and B-cell response, and provide effective protection against RSV infection in mice. Importantly, dsRNA adjuvants significantly enhanced T-cell immune responses and increased neutralizing antibody levels when administered via oral vaccination (P<0.05). These preclinical data demonstrate the capacity of an oral vaccine to induce protective immunity against RSV and support further development of RSV vaccine.

Preliminary Study on Type I Interferon as a Mucosal Adjuvant for Human Respiratory Syncytial Virus F Protein.

Background: Human respiratory syncytial virus (HRSV) imposes a significant disease burden on infants and the elderly. Intranasal immunization using attenuated live vaccines and certain vector vaccines against HRSV has completed phase II clinical trials with good safety and efficacy.Recombinant protein vaccines for mucosal immunization require potent mucosal adjuvants. Type I interferon (IFN), as a natural mucosal adjuvant, significantly enhances antigen-presenting cell processing and antigen presentation, promoting the production of T and B cells. Methods: This study utilized human α2b interferon (IFN-human) and mouse α2 interferon (IFN-mouse) as nasal mucosal adjuvants in combination with fusion protein (F). Intranasal immunization was performed on BALB/c mice to evaluate the immunogenicity of the formulation in vivo. Results: Compared to the F protein immunization group, mice in the F + IFN-Human and F + IFN-Mouse experimental groups exhibited significantly increased neutralizing antibody titers and augmented secretion of IFN-γ and IL-4 by lymphocytes, and both of them could induce the production of high-titer specific IgA antibodies in mice (p < 0.001).The F + IFN-Human immunization induced the highest IgG and IgG1 antibody titers in mice; however, the F + IFN-Mouse immunization group elicited the highest neutralizing antibody titers (598), lowest viral loads in the lungs (Ct value of 31), and fastest weight recovery in mice. Moreover, mice in the F + IFN-Mouse immunization group displayed the mildest lung pathological damage (Total score of pathological injury was 2). Conclusions: In conclusion, IFN-Mouse, as a mucosal adjuvant for HRSV recombinant protein vaccines, demonstrated superior protective effects in mice compared to IFN-Human adjuvants.

Immunogenicity of the Monovalent Omicron XBB.1.5-Adapted BNT162b2 COVID-19 Vaccine in People Living with HIV (PLWH).

While SARS-CoV-2 has transitioned to an endemic phase, infections caused by newly emerged variants continue to result in severe, and sometimes fatal, outcomes or lead to long-term COVID-19 symptoms. Vulnerable populations, such as PLWH, face an elevated risk of severe illness. Emerging variants of SARS-CoV-2, including numerous Omicron subvariants, are increasingly associated with breakthrough infections. Adapting mRNA vaccines to these new variants may offer improved protection against Omicron for vulnerable individuals. In this study, we examined humoral and cellular immune responses before and after administering adapted booster vaccinations to PLWH, alongside a control group of healthy individuals. Four weeks following booster vaccination, both groups exhibited a significant increase in neutralizing antibodies and cellular immune responses. Notably, there was no significant difference in humoral immune response between PLWH and the healthy controls. Immune responses declined rapidly in both groups three months post vaccination. However, PLWH still showed significantly increased neutralizing antibody titers even after three months. These findings demonstrate the efficacy of the adapted vaccination regimen. The results suggest that regular booster immunizations may be necessary to sustain protective immunity.

Controlled Reduction of Reactogenicity in Vaccines - Designing New Molecules to Alter Innate Signal Processing

Abstract Vaccines are a critical tool in preventing and managing many diseases, but their efficacy can be improved by enhancing their immunogenicity and lowering their reactogenicity. We have developed a series of molecules that directly reduce correlates of reactogenicity while also improving protection. We present data on the application of these immunomodulator towards a CpG adjuvanted subunit SARS- CoV-2 vaccine in both mice and Syrian hamsters. Immunomodulator-containing vaccines increased neutralizing antibody and T-cell responses in mice. In a challenge model in hamsters, these vaccines reduced weight loss, viral load, and tissue damage. These findings demonstrate the possible improvement of current and future vaccines using immunomodulators. We also present a series of modulators that reduce and direct inflammatory responses in a controlled fashion for use in influenza, hepatitis, typhoid, and many other vaccine applications.

Clearance of persistent SARS-CoV-2 associates with increased neutralizing antibodies in advanced HIV disease post-ART initiation

SARS-CoV-2 clearance requires adaptive immunity but the contribution of neutralizing antibodies and T cells in different immune states is unclear. Here we ask which adaptive immune responses associate with clearance of long-term SARS-CoV-2 infection in HIV-mediated immunosuppression after suppressive antiretroviral therapy (ART) initiation. We assembled a cohort of SARS-CoV-2 infected people in South Africa (n = 994) including participants with advanced HIV disease characterized by immunosuppression due to T cell depletion. Fifty-four percent of participants with advanced HIV disease had prolonged SARS-CoV-2 infection (>1 month). In the five vaccinated participants with advanced HIV disease tested, SARS-CoV-2 clearance associates with emergence of neutralizing antibodies but not SARS-CoV-2 specific CD8 T cells, while CD4 T cell responses were not determined due to low cell numbers. Further, complete HIV suppression is not required for clearance, although it is necessary for an effective vaccine response. Persistent SARS-CoV-2 infection led to SARS-CoV-2 evolution, including virus with extensive neutralization escape in a Delta variant infected participant. The results provide evidence that neutralizing antibodies are required for SARS-CoV-2 clearance in HIV-mediated immunosuppression recovery, and that suppressive ART is necessary to curtail evolution of co-infecting pathogens to reduce individual health consequences as well as public health risk linked with generation of escape mutants.

SARS-CoV-2 Neutralization Capacity in Hemodialysis Patients with and without a Fifth Vaccination with the Updated Comirnaty Original/Omicron BA.4-5 Vaccine.

Hemodialysis patients have reduced serologic immunity after SARS-CoV-2 vaccination compared to the general population and an increased risk of morbidity and mortality when exposed to SARS-CoV-2. Sixty-six hemodialysis patients immunized four times with the original SARS-CoV-2 vaccines (BNT162b2, mRNA-1273) either received a booster with the adapted Comirnaty Original/Omicron BA.4-5 vaccine 8.3 months after the fourth vaccination and/or experienced a breakthrough infection. Two months before and four weeks after the fifth vaccination, the live-virus neutralization capacities of Omicron variants BA.5, BQ.1.1, and XBB.1.5 were determined, as well as neutralizing and quantitative anti-SARS-CoV-2 spike-specific IgG antibodies. Four weeks after the fifth vaccination with the adapted vaccine, significantly increased neutralizing antibodies and the neutralization of Omicron variants BA.5, BQ.1.1, and XBB.1.5 were observed. The increase was significantly higher than after the fourth vaccination for variants BQ.1.1 and BA.5. Of all analyzed variants, BA.5 was neutralized best after the fifth vaccination. We did not see a difference in humoral immunity between the group with an infection and the group with a vaccination as a fifth spike exposure. Fivefold-vaccinated patients with a breakthrough infection showed a significantly higher neutralization capacity of XBB.1.5. A fifth SARS-CoV-2 vaccination with the adapted vaccine improves both wild-type specific antibody titers and the neutralizing capacity of the current Omicron variants BA.5, BQ.1.1, and XBB.1.5 in hemodialysis patients. Additional booster vaccinations with adapted vaccines will likely improve immunity towards current and original SARS-CoV-2 variants and are, therefore, recommended in hemodialysis patients. Further longitudinal studies must show the extent to which this booster vaccination avoids a breakthrough infection.

Safety and Immunogenicity of a Messenger RNA-Based Cytomegalovirus Vaccine in Healthy Adults: Results From a Phase 1 Randomized Clinical Trial.

This phase 1 trial evaluated the safety, reactogenicity, and immunogenicity of mRNA-1647, a messenger RNA (mRNA)-based cytomegalovirus (CMV) vaccine, in CMV-seronegative and -seropositive adults. Participants were randomly assigned to receive 30, 90, 180, or 300 µg of mRNA-1647 or placebo on a 0-, 2-, and 6-month schedule and followed for 12 months after the last dose. A total of 154 (80 CMV-seronegative and 74 CMV-seropositive) participants were enrolled; 118 participants were randomized to mRNA-1647 and 36 to placebo. Mean (standard deviation) age was 32.5 (8.6) and 35.1 (8.9) years in the placebo and mRNA-1647 groups, respectively, in phase B (63% and 64% female) and 42.5 (6.2) and 33.3 (8.7) years, respectively, in phase C (2% and 16% female). No deaths, related serious adverse events, or adverse events of special interest were reported. Most adverse reactions were grade ≤2 severity. Increased neutralizing antibody, binding antibody, and antigen-specific cell-mediated responses were observed across mRNA-1647 treatment groups, regardless of CMV serostatus. This phase 1, first-in-human trial demonstrated that mRNA-1647 has an acceptable safety profile in adults and elicits humoral and cellular immune responses. Clinical Trials Registration. NCT03382405.

Preliminary Study on the Efficacy of a Recombinant, Subunit SARS-CoV-2 Animal Vaccine against Virulent SARS-CoV-2 Challenge in Cats.

The objective of this work was to evaluate the safety and efficacy of a recombinant, subunit SARS-CoV-2 animal vaccine in cats against virulent SARS-CoV-2 challenge. Two groups of cats were immunized with two doses of either a recombinant SARS-CoV-2 spike protein vaccine or a placebo, administered three weeks apart. Seven weeks after the second vaccination, both groups of cats were challenged with SARS-CoV-2 via the intranasal and oral routes simultaneously. Animals were monitored for 14 days post-infection for clinical signs and viral shedding before being humanely euthanized and evaluated for macroscopic and microscopic lesions. The recombinant SARS-CoV-2 spike protein subunit vaccine induced strong serologic responses post-vaccination and significantly increased neutralizing antibody responses post-challenge. A significant difference in nasal and oral viral shedding, with significantly reduced virus load (detected using RT-qPCR) was observed in vaccinates compared to mock-vaccinated controls. Duration of nasal, oral, and rectal viral shedding was also significantly reduced in vaccinates compared to controls. No differences in histopathological lesion scores were noted between the two groups. Our findings support the safety and efficacy of the recombinant spike protein-based SARS-CoV-2 vaccine which induced high levels of neutralizing antibodies and reduced nasal, oral, and rectal viral shedding, indicating that this vaccine will be efficacious as a COVID-19 vaccine for domestic cats.

The fourth COVID-19 vaccine dose increased the neutralizing antibody response against the SARS-CoV-2 Omicron (B.1.1.529) variant in a diverse Brazilian population.

Most of the original immunization regimens against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) were composed of two doses, followed by a subsequent third booster dose to control the Omicron variant and hence coronavirus disease 2019 (COVID-19). However, most data generated regarding the fourth dose were not based on the general population. Therefore, this study aimed to verify the effect of the fourth COVID-19 vaccine dose in a diverse Brazilian population. This retrospective observational study was conducted between May and September 2022. We gathered data on the vaccine regimens and COVID-19 serologic status from 266 healthy volunteers who received three or four vaccine doses, as well as COVID-19 diagnosis and viral genome sequencing from 457 patients with flu-like symptoms. In addition, we conducted immunoinformatic analysis to assess the conserved epitopes in the locally circulating viruses. We showed that the fourth dose did not increase the serum levels of antiviral antibodies, as measured by enzyme-linked immunosorbent assay. However, it significantly increased neutralizing antibody (NAb) titers against the Omicron variant. All viral sequences generated in this study were Omicron subvariants, mainly B.A.5.1. Notably, most NAb epitopes present in the wild-type SARS-CoV-2 were not detected among the circulating Omicron subvariants. None of the volunteers who received the third or fourth doses presented COVID-19 for at least 1 year before the study period. Altogether, these results indicate that the fourth vaccine dose increases the serum levels of NAbs that recognize highly conserved epitopes in Omicron subvariants.IMPORTANCESeveral additional COVID-19 vaccine doses were administered in the Brazilian population to prevent the disease caused by the B.1.1.529 (Omicron) variant. The efficacy of a third dose as a booster is already well described. However, it is important to clarify the humoral immune response gain induced by a fourth dose. In this study, we evaluate the effect of the fourth COVID-19 vaccine dose in a diverse Brazilian population, considering a real-life context. Our study reveals that the fourth dose of the COVID-19 vaccine increased the neutralizing antibody response against SARS-CoV-2 Omicron and significantly contributed in the reduction of the disease caused by this variant.

Third COVID-19 vaccine dose boosts antibody function in Rwandans with high HIV viral load

SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) causing COVID-19 (coronavirus disease 2019) poses a greater health risk to immunocompromized individuals including people living with HIV (PLWH). However, most studies on PLWH have been conducted in higher-income countries. We investigated the post-vaccination antibody responses of PLWH in Rwanda by collecting peripheral blood from participants after receiving a second or third COVID-19 vaccine. Virus-binding antibodies as well as antibody neutralization ability against all major SARS-CoV-2 variants of concern were analyzed. We found that people with high HIV viral loads and two COVID-19 vaccine doses had lower levels of binding antibodies that were less virus neutralizing and less cross-reactive compared to control groups. A third vaccination increased neutralizing antibody titers. Our data suggest that people with high HIV viral loads require a third dose of vaccine to neutralize SARS-CoV-2 virus and new variants as they emerge.

Association of selenium profile with neutralizing antibody response to inactivated SARS-CoV-2 vaccination

BackgroundSelenium profile has been related with humoral immune response after vaccination, but evidence with regard to inactivated SARS-CoV-2 vaccine is lacking. ObjectiveThe current study aimed to examine the relationship between selenium profile and neutralizing antibody response to inactivated SARS-CoV-2 vaccine. MethodsPlasma selenium and selenoprotein P concentrations, neutralizing antibody against the wild-type and Omicron variant were measured at baseline and at 14 days, 98 days after the third dose of inactivated SARS-CoV-2 vaccine. ResultsNeutralizing antibody against the wild-type and Omicron variant increased significantly after the third vaccination dose. Both higher plasma selenium and selenoprotein P were associated with increased neutralizing antibody against the wild-type strain at baseline. Moreover, higher plasma selenoprotein P was associated with increased neutralizing antibody against Omicron variant at baseline. However, nonsignificant association were observed after the third vaccine dose. ConclusionHigher selenium profile was associated with neutralizing antibody response before the third dose of inactivated SARS-CoV-2 vaccine, but not after the third dose. Further prospective cohort studies are warranted to confirm our findings.

Monovalent SARS-CoV-2 mRNA Vaccine Does not Boost Omicron-Specific Immune Response in Diabetic and Control Pediatric Patients.

While the immunogenicity of SARS-CoV-2 vaccines has been well described in adults, pediatric populations have been less studied. In particular, children with type 1 diabetes are generally at elevated risk for more severe disease after infections, but are understudied in terms of COVID-19 and SARS-CoV-2 vaccine responses. We investigated the immunogenicity of COVID-19 mRNA vaccinations in 35 children with type 1 diabetes (T1D) and 23 controls and found that these children develop levels of SARS-CoV-2 neutralizing antibody titers and spike protein-specific T cells comparable to nondiabetic children. However, in comparing the neutralizing antibody responses in children who received 2 doses of mRNA vaccines (24 T1D; 14 controls) with those who received a third, booster dose (11 T1D; 9 controls), we found that the booster dose increased neutralizing antibody titers against ancestral SARS-CoV-2 strains but, unexpectedly, not Omicron lineage variants. In contrast, boosting enhanced Omicron variant neutralizing antibody titers in adults.

Correlates of protection for booster doses of the SARS-CoV-2 vaccine BNT162b2

Vaccination, especially with multiple doses, provides substantial population-level protection against COVID-19, but emerging variants of concern (VOC) and waning immunity represent significant risks at the individual level. Here we identify correlates of protection (COP) in a multicenter prospective study following 607 healthy individuals who received three doses of the Pfizer-BNT162b2 vaccine approximately six months prior to enrollment. We compared 242 individuals who received a fourth dose to 365 who did not. Within 90 days of enrollment, 239 individuals contracted COVID-19, 45% of the 3-dose group and 30% of the four-dose group. The fourth dose elicited a significant rise in antibody binding and neutralizing titers against multiple VOCs reducing the risk of symptomatic infection by 37% [95%CI, 15%-54%]. However, a group of individuals, characterized by low baseline titers of binding antibodies, remained susceptible to infection despite significantly increased neutralizing antibody titers upon boosting. A combination of reduced IgG levels to RBD mutants and reduced VOC-recognizing IgA antibodies represented the strongest COP in both the 3-dose group (HR = 6.34, p = 0.008) and four-dose group (HR = 8.14, p = 0.018). We validated our findings in an independent second cohort. In summary combination IgA and IgG baseline binding antibody levels may identify individuals most at risk from future infections.

Immune responses in COVID-19 patients during breakthrough infection with SARS-CoV-2 variants Delta, Omicron-BA.1 and Omicron-BA.5.

Breakthrough infections with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants are increasingly observed in vaccinated individuals. Immune responses towards SARS-CoV-2 variants, particularly Omicron-BA.5, are poorly understood. We investigated the humoral and cellular immune responses of hospitalized COVID-19 patients during Delta and Omicron infection waves. The corresponding SARS-CoV-2 variant of the respective patients were identified by whole genome sequencing. Humoral immune responses were analyzed by ELISA and a cell culture-based neutralization assay against SARS-CoV-2 D614G isolate (wildtype), Alpha, Delta (AY.43) and Omicron (BA.1 and BA.5). Cellular immunity was evaluated with an IFN-γ ELISpot assay. On a cellular level, patients showed a minor IFN-γ response after stimulating PBMCs with mutated regions of SARS-CoV-2 variants. Neutralizing antibody titers against Omicron-BA.1 and especially BA.5 were strongly reduced. Double-vaccinated patients with Delta breakthrough infection showed a significantly increased neutralizing antibody response against Delta compared to double-vaccinated uninfected controls (median complete neutralization titer (NT100) 640 versus 80, p<0.05). Omicron-BA.1 infection increased neutralization titers against BA.1 in double-vaccinated patients (median NT100 of 160 in patients versus 20 in controls, p=0.07) and patients that received booster vaccination (median NT100 of 50 in patients versus 20 in controls, p=0.68). For boosted patients with BA.5 breakthrough infection, we found no enhancing effect on humoral immunity against SARS-CoV-2 variants. Neutralizing antibody titers against Omicron-BA.1 and especially BA.5 were strongly reduced in SARS-CoV-2 breakthrough infections. Delta and Omicron-BA.1 but not Omicron-BA.5 infections boosted the humoral immunity in double-vaccinated patients and patients with booster vaccination. Despite BA.5 breakthrough infection, those patients may still be vulnerable for reinfections with BA.5 or other newly emerging variants of concern.

Neutralization sensitivity, fusogenicity, and infectivity of Omicron subvariants

BackgroundThe emergence of SARS-CoV-2 Omicron subvariants has raised questions regarding resistance to immunity by natural infection or immunization. We examined the sensitivity of Delta and Omicron subvariants (BA.1, BA.1.1, BA.2, BA.2.12.1, BA.4/5, and BA.3) to neutralizing antibodies from BBIBP-CorV-vaccinated and BBIBP-CorV- or ZF2001-boosted individuals, as well as individuals with Delta and BA.1 breakthrough infections, and determined their fusogenicity and infectivity.MethodsIn this cross-sectional study, serum samples from two doses of BBIBP-CorV-vaccinated individuals 1 (n = 36), 3 (n = 36), and 7 (n = 37) months after the second dose; BBIBP-CorV- (n = 25) or ZF2001-boosted (n = 30) individuals; and fully vaccinated individuals with Delta (n = 30) or BA.1 (n = 26) infection were collected. The serum-neutralizing reactivity and potency of bebtelovimab were assessed against D614G, Delta, and Omicron subvariants (BA.1, BA.1.1, BA.2, BA.2.12.1, BA.4/5, and BA.3) through a pseudovirus neutralization assay. The fusogenicity and infectivity of D614G, Delta, and Omicron subvariants were determined by cell-cell fusion assay and pseudovirus infection assay, respectively.ResultsOmicron subvariants markedly escaped vaccine-elicited neutralizing antibodies after two doses of BBIBP-CorV with comparable efficiency. A third dose vaccination of BBIBP-CorV or ZF2001 increased neutralizing antibody titers and breadth against Delta and three Omicron subvariants. Delta and BA.1 breakthrough infections induced comparable neutralizing antibody titers against D614G and Delta variants, whereas BA.1 breakthrough infections elicited a stronger and broader antibody response against three Omicron subvariants than Delta breakthrough infections. BA.2.12.1 and BA.4/5 are more resistant to immunity induced by breakthrough infections. Bebtelovimab had no significant loss of potency against the Delta and Omicron subvariants. Cell culture experiments showed Omicron subvariants to be less fusogenic and have higher infectivity than D614G and Delta with comparable efficiency.ConclusionsThese findings have important public health implications and highlight the importance of repeated exposure to SARS-CoV-2 antigens to broaden the neutralizing antibody response against Omicron subvariants.

1974. Title: A novel low-dose self-amplifying mRNA vaccine (GRT-R910) induces strong and broad boost in cellular and humoral immune response following primary series with a chimpanzee adenovirus SARS-CoV-2 vaccination

Abstract Disclosures Ciaran Scallan, PhD, Gritstone Bio: Salaried employee of Gritstone|Gritstone Bio: Stocks/Bonds Andrew Ustianowski, MD, PhD, Gilead: Advisor/Consultant|Gilead: Board Member|Gilead: Honoraria|Gilead: Speaker fees|Pfizer: Honoraria|Pfizer: Speaker fees|Vir/GlaxoSmithKline: Advisor/Consultant|Vir/GlaxoSmithKline: Board Member. Background The SARS-CoV-2 pandemic continues, with new variants of concern fueling periodic increases in COVID-19 cases. Authorized vaccines have provided protection against severe disease but less so for incident cases. Boosts with these vaccines have demonstrated waning protection. New vaccines, including those which induce immunity against more conserved regions outside of Spike, may improve upon these and be key to long-term protection and may be a useful approach against novel coronaviruses. Methods GO-009 (CORAL-Boost, NCT05148962) is an open-label study, conducted in the UK, of a self-amplifying mRNA vaccine encoding for Wuhan Spike (S) and highly conserved non-S T cell epitopes (GRT-R910; R910). R910 is given as 1 or 2 doses after vaccination with an authorized adenovirus or mRNA SARS-CoV-2 vaccine. The first two cohorts assessed 10µg and 30µg doses of R910 in older (≥60y) adults who had previously received ChAdOx1. Subsequent cohorts assess two boost doses in older and younger adults who have received an adenovirus or mRNA vaccine. Primary objectives are safety and reactogenicity and secondary objectives include cellular and humoral immunogenicity. Results Ten and seven adults received 10 or 30µg (cohorts 1 and 2) of R910, respectively. Reactogenicity and unsolicited adverse events were mostly mild/moderate and transient. The majority of severe events (malaise, fatigue, myalgia, Inj. site pain/tenderness/swelling) after dose 1 were experienced by 1 subject in cohort 2. Analysis of both IgG binding and neutralizing antibodies demonstrated a boost of anti-S antibodies after one dose of R910; geomean ID50 titers from 92 to 2370 and 99 to 1553 for 10 and 30µg, respectively. ELISpot analyses demonstrated that R910 boosted and broadened T cell responses to S and non-S T cell epitopes. Conclusion R910 was well tolerated. One R910 boost vaccination increased existing humoral and cellular immunity against S while inducing a broad T cell response against non-S SARS-CoV-2 proteins. A 10µg R910 boost increased neutralizing antibody titers comparable to a 10-fold higher dose (100µg) with authorized mRNA vaccines in a similar population (Munro et al 2021). A 10µg dose was selected for further study. Data post mRNA primary series will also be presented.

High titre neutralizing antibodies in response to SARS-CoV-2 infection require RBD-specific CD4 T cells that include proliferative memory cells.

Long-term immunity to SARS-CoV-2 infection, including neutralizing antibodies and T cell-mediated immunity, is required in a very large majority of the population in order to reduce ongoing disease burden. We have investigated the association between memory CD4 and CD8 T cells and levels of neutralizing antibodies in convalescent COVID-19 subjects. Higher titres of convalescent neutralizing antibodies were associated with significantly higher levels of RBD-specific CD4 T cells, including specific memory cells that proliferated vigorously in vitro. Conversely, up to half of convalescent individuals had low neutralizing antibody titres together with a lack of receptor binding domain (RBD)-specific memory CD4 T cells. These low antibody subjects had other, non-RBD, spike-specific CD4 T cells, but with more of an inhibitory Foxp3+ and CTLA-4+ cell phenotype, in contrast to the effector T-bet+, cytotoxic granzymes+ and perforin+ cells seen in RBD-specific memory CD4 T cells from high antibody subjects. Single cell transcriptomics of antigen-specific CD4+ T cells from high antibody subjects similarly revealed heterogenous RBD-specific CD4+ T cells that comprised central memory, transitional memory and Tregs, as well as cytotoxic clusters containing diverse TCR repertoires, in individuals with high antibody levels. However, vaccination of low antibody convalescent individuals led to a slight but significant improvement in RBD-specific memory CD4 T cells and increased neutralizing antibody titres. Our results suggest that targeting CD4 T cell epitopes proximal to and within the RBD-region should be prioritized in booster vaccines.

An evaluation of intradermal all-in-one vaccine based on an inactivated recombinant Mycoplasma hyopneumoniae strain expressing porcine circovirus type 2 (PCV2) capsid protein against Korean stains of PCV2d and M. hyopneumoniae challenge

This study evaluates the efficacy of intradermal all-in-one vaccine (MHYOSPHERE® PCV ID, Laboratorios Hipra S.A. Amer, Spain) based on the strain Nexhyon, an inactivated recombinant M. hyopneumoniae strain with an embedded/integrated PCV2a capsid protein thereof, as the single active substance. Pigs were administered the vaccine intradermally at 21 days of age with 0.2 mL, then challenged at 49 days of age with either M. hyopneumoniae (intratracheal route), PCV2d (intranasal route), or both. Upon dual challenge, growth performance was improved when the intradermal all in one vaccine was administered compared to the unvaccinated group. In pigs receiving single or dual challenge, vaccination increased neutralizing antibodies against PCV2d and specific interferon-γ secreting cells for each pathogen. In contrast, viral load of PCV2d in the blood, M. hyopneumoniae load in the larynx, and the severity of pulmonary and lymphoid lesions were decreased. Vaccination provided good protection against challenge with M. hyopneumoniae and PCV2d.