SARS-COV-2 recombinant Receptor-Binding-Domain (RBD) induces neutralizing antibodies against variant strains of SARS-CoV-2 and SARS-CoV-1

Safety and immunogenicity of SARS-CoV-2 protein subunit recombinant vaccine (Indovac®) in healthy populations aged 18 years and above in Indonesia: A phase I, observer-blind, randomized, controlled study

Indonesian vaccine producer (PT BIOFARMA), conducted a study to assess the safety and immunogenicity of a new COVID-19 vaccine candidate. This vaccine is based on a recombinant subunit protein platform, with the SARS-CoV-2 receptor-binding domain (RBD) as its target antigen. The study compared the candidate's safety and immunogenicity to the control group vaccine, the Sinovac vaccine, 28 days after administration. This was an observer-blinded and randomized Phase 1 trial which recruited 175 subjects. The subject received 0.5 ml of vaccine in two doses. The subjects were split into five treatment groups, consisting of different combinations of doses between RBD and CpG. The safety of this vaccine was evaluated within 7 days after the first dose and for 6 months after the second dose, while the immunogenicity was evaluated on days 14 and 28 after the second dose. The overall incidence of AEs was 54.86% from the beginning of the vaccination to 28 days after each injection. Most AEs were local pain and had no serious AEs. The study revealed a significant rise in the Geometric Mean Titer (GMT) of IgG antibodies in every group, indicating a strong immune response. The phase I data demonstrated that the new vaccine candidate showed promising results in safety and immunogenicity.

On the adjuvanticity of hyaluronan: The case of a SARS-CoV-2 vaccine

Vaccines based on mRNA have been fundamental in facing the COVID-19 pandemic, however, they still raise concerns about stability and long-term efficacy. Thus, protein-based vaccines remain valid options and hence the study of effective adjuvants is crucial. Here, we developed a COVID-19 vaccine based on the receptor-binding domain (RBD) of SARS-CoV-2 Spike protein, which is covalently conjugated to the natural polymer hyaluronan (HA) that acts as an immunological adjuvant. Vaccination of K18-hACE2 mice with HA-RBD was well tolerated, and elicited high and sustained titres of RBD-binding antibodies and SARS-CoV-2-neutralizing antibodies, without the addition of other immunostimulatory compounds. Most importantly, HA-RBD vaccination conferred long-term protection to K18-hACE2 mice after challenge with SARS-CoV-2, also in the case of two consequent infections driven by different variants. These findings demonstrate the efficacy of HA-based vaccination against COVID-19 disease, and support the promising use of HA as an efficient and well tolerated adjuvant.

Beyond the Pandemic Era: Recent Advances and Efficacy of SARS-CoV-2 Vaccines Against Emerging Variants of Concern

Vaccination has been instrumental in curbing the transmission of SARS-CoV-2 and mitigating the severity of clinical manifestations associated with COVID-19. Numerous COVID-19 vaccines have been developed to this effect, including BioNTech-Pfizer and Moderna's mRNA vaccines, as well as adenovirus vector-based vaccines such as Oxford-AstraZeneca. However, the emergence of new variants and subvariants of SARS-CoV-2, characterized by enhanced transmissibility and immune evasion, poses significant challenges to the efficacy of current vaccination strategies. In this review, we aim to comprehensively outline the landscape of emerging SARS-CoV-2 variants of concern (VOCs) and sub-lineages that have recently surfaced in the post-pandemic years. We assess the effectiveness of existing vaccines, including their booster doses, against these emerging variants and subvariants, such as BA.2-derived sub-lineages, XBB sub-lineages, and BA.2.86 (Pirola). Furthermore, we discuss the latest advancements in vaccine technology, including multivalent and pan-coronavirus approaches, along with the development of several next-generation coronavirus vaccines, such as exosome-based, virus-like particle (VLP), mucosal, and nanomaterial-based vaccines. Finally, we highlight the key challenges and critical areas for future research to address the evolving threat of SARS-CoV-2 subvariants and to develop strategies for combating the emergence of new viral threats, thereby improving preparedness for future pandemics.

Docking heparan sulfate-based ligands as a promising inhibitor for SARS-CoV-2

CONTEXT

Heparan sulfate (HS) linear polysaccharide glycosaminoglycan compound is linked to components from the cell surface and the extracellular matrix. HS mediates SARS-CoV-2 infection through spike protein binding to cell surface receptors and is required to bind ACE2, prompting the need for electronic structure and molecular docking evaluation of this core system to exploit this attachment in developing new derivatives. Therefore, we have studied five molecules based on HS using molecular docking and electronic structure analysis. Non-covalent interaction analysis shows hydrogen bonding and van der Waals interactions in the binding to RBD-ACE2 interface and 3CLpro. SDM3 and SDM1 molecules present the lowest gap, including solvent effect under 154.6 kcal/mol, and exhibit the most reactivity behavior in this group, potentially leading to enhanced interaction in docking studies.

METHODS

Heparan sulfate and four derivatives were optimized using B3LYP functional with two basis sets 6-31 + G(d,p) and def2SVP. Electronic structure was used to explore the main interactions and the reactivity of these molecules, and these optimized structures were used in the molecular docking study against 3CLpro, RBD, and ACE2.

Expression of the SARS-CoV-2 receptor-binding domain by live attenuated influenza vaccine virus as a strategy for designing a bivalent vaccine against COVID-19 and influenza

Influenza and SARS-CoV-2 are two major respiratory pathogens that cocirculate in humans and cause serious illness with the potential to exacerbate disease in the event of co-infection. To develop a bivalent vaccine, capable of protecting against both infections, we inserted the receptor-binding domain (RBD) of the SARS-CoV-2 spike protein into hemagglutinin (HA) molecule or into the open reading frame of the truncated nonstructural protein 1 (NS1) of live attenuated influenza vaccine (LAIV) virus and assessed phenotypic characteristics of the rescued LAIV-RBD viruses, as well as their immunogenicity in mouse and Syrian hamster animal models. A panel of 9 recombinant LAIV-RBD viruses was rescued using the A/Leningrad/17 backbone. Notably, only two variants with RBD insertions into the HA molecule could express sufficient quantities of RBD protein in infected MDCK cells. Intranasal immunization of mice induced high levels of anti-influenza antibody responses in all chimeric LAIV-RBD viruses, which was comparable to the LAIV virus vector. The RBD-specific antibody responses were most pronounced in the variant expressing RBD194 fragment as a chimeric HA protein. This candidate was further tested in Syrian hamsters and was shown to be immunogenic and capable of protecting animals against both infections.

Immunogenicity studies of recombinant RBD SARS-CoV-2 as a COVID-19 vaccine candidate produced in Escherichia coli

The severe acute respiratory syndrome coronavirus 2 -related global COVID-19 pandemic has been impacting millions of people since its outbreak in 2020. COVID-19 vaccination has proven highly efficient in reducing illness severity and preventing infection-related fatalities. The World Health Organization has granted emergency use approval to multiple, including protein subunit technology-based, COVID-19 vaccines. Foreseeably, additional COVID-19 subunit vaccine development would be essential to meet the accessible and growing demand for effective vaccines, especially for Low-Middle-Income Countries (LMIC). The SARS-CoV-2 spike protein receptor binding domain (RBD), as the primary target for neutralizing antibodies, holds significant potential for future COVID-19 subunit vaccine development. In this study, we developed a recombinant Escherichia coli-expressed RBD (rRBD) as a vaccine candidate and evaluated its immunogenicity and preliminary toxicity in BALB/c mice. The rRBD induced humoral immune response from day 7 post-vaccination and, following the booster doses, the IgG levels increased dramatically in mice. Interestingly, our vaccine candidate also significantly induced cellular immune response, indicated by the incrased IFN-ɣ-producing cell numbers. We observed no adverse effect or local reactogenicity either in control or treated mice. Taken together, our discoveries could potentially support efficient and cost-effective vaccine antigen production, from which LMICs could particularly benefit.

Immunoinformatics-aided rational design of a multi-epitope vaccine targeting feline infectious peritonitis virus

Feline infectious peritonitis (FIP) is a grave and frequently lethal ailment instigated by feline coronavirus (FCoV) in wild and domestic feline species. The spike (S) protein of FCoV assumes a critical function in viral ingress and infection, thereby presenting a promising avenue for the development of a vaccine. In this investigation, an immunoinformatics approach was employed to ascertain immunogenic epitopes within the S-protein of FIP and formulate an innovative vaccine candidate. By subjecting the amino acid sequence of the FIP S-protein to computational scrutiny, MHC-I binding T-cell epitopes were predicted, which were subsequently evaluated for their antigenicity, toxicity, and allergenicity through in silico tools. Our analyses yielded the identification of 11 potential epitopes capable of provoking a robust immune response against FIPV. Additionally, molecular docking analysis demonstrated the ability of these epitopes to bind with feline MHC class I molecules. Through the utilization of suitable linkers, these epitopes, along with adjuvants, were integrated to design a multi-epitope vaccine candidate. Furthermore, the stability of the interaction between the vaccine candidate and feline Toll-like receptor 4 (TLR4) was established via molecular docking and molecular dynamics simulation analyses. This suggests good prospects for future experimental validation to ascertain the efficacy of our vaccine candidate in inducing a protective immune response against FIP.

Pre-Clinical Safety and Immunogenicity Study of a Coronavirus Protein-Based Subunit Vaccine for COVID-19

Creating an effective and safe vaccine is critical to fighting the coronavirus infection successfully. Several types of COVID-19 vaccines exist, including inactivated, live attenuated, recombinant, synthetic peptide, virus-like particle-based, DNA and mRNA-based, and sub-unit vaccines containing purified immunogenic viral proteins. However, the scale and speed at which COVID-19 is spreading demonstrate a global public demand for an effective prophylaxis that must be supplied more. The developed products promise a bright future for SARS-CoV-2 prevention; however, evidence of safety and immunogenicity is mandatory before any vaccine can be produced. In this paper, we report on the results of our work examining the safety, toxicity, immunizing dose choice, and immunogenicity of QazCoVac-P, a Kazakhstan-made sub-unit vaccine for COVID-19. First, we looked into the product's safety profile by assessing its pyrogenicity in vaccinated rabbit models and using the LAL (limulus amebocyte lysate) test. We examined the vaccine's acute and sub-chronic toxicity on BALB/c mice and rats. The vaccine did not cause clinically significant toxicity-related changes or symptoms in our toxicity experiments. Finally, we performed a double immunization of mice, ferrets, Syrian hamsters, and rhesus macaques (Macaca mulatta). We used ELISA to measure antibody titers with the maximum mean geometric titer of antibodies in the animals' blood sera totaling approximately 8 log2. The results of this and other studies warrant recommending the QazCoVac-P vaccine for clinical trials.

The Influence of Adjuvant Type on the Immunogenicity of RBD/N Cocktail Antigens as a Vaccine Candidate against SARS-CoV-2 Virus

The emerging virus SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus 2 virus), agent of COVID-19, appeared in December 2019 in Wuhan, China, and became a serious threat to global health and public safety. Many COVID-19 vaccines have been approved and licensed around the world. Most of the developed vaccines include S protein and induce an antibody-based immune response. Additionally, T-cell response to the SARS-CoV-2 antigens could be beneficial for combating the infection. The type of immune response is greatly dependent not only on the antigen, but also on adjuvants used in vaccine formulation. Here, we compared the effect of four different adjuvants (AddaS03, Alhydrogel/MPLA, Alhydrogel/ODN2395, Quil A) on the immunogenicity of a mixture of recombinant RBD and N SARS-CoV-2 proteins. We have analyzed the antibody and T-cell response specific to RBD and N proteins and assessed the impact of adjuvants on virus neutralization. Our results clearly indicated that Alhydrogel/MPLA and Alhydrogel/ODN2395 adjuvants elicited the higher titers of specific and cross-reactive antibodies to S protein variants from various SARS-CoV-2 and SARS-CoV-1 strains. Moreover, Alhydrogel/ODN2395 stimulated high cellular response to both antigens, as assessed by IFN-γ production. Importantly, sera collected from mice immunized with RBD/N cocktail in combination with these adjuvants exhibited neutralizing activity against the authentic SARS-CoV-2 virus as well as particles pseudotyped with S protein from various virus variants. The results from our study demonstrate the immunogenic potential of RBD and N antigens and point out the importance of adjuvants selection in vaccine formulation in order to enhance the immunological response. IMPORTANCE Although several COVID-19 vaccines have been approved worldwide, continuous emergence of new SARS-CoV-2 variants calls for new efficient vaccines against them, providing long-lasting immunity. As the immune response after vaccination is dependent not only on antigen used, but also on other vaccine components, e.g., adjuvants, the purpose of this work was to study the effect of different adjuvants on the immunogenicity of RBD/N SARS-CoV-2 cocktail proteins. In this work, it has been shown that immunization with both antigens plus the different adjuvants studied elicited higher Th1 and Th2 responses against RBD and N, which contributed to higher neutralization of the virus. The obtained results can be used for design of new vaccines, not only against SARS-CoV-2, but also against other important viral pathogens.

Bovine Serum Albumin-Protected Gold Nanoclusters for Sensing of SARS-CoV-2 Antibodies and Virus

An approach to assess severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection (and past infection) was developed. For virus detection, the SARS-CoV-2 virus nucleocapsid protein (NP) was targeted. To detect the NP, antibodies were immobilized on magnetic beads to capture the NPs, which were subsequently detected using rabbit anti-SARS-CoV-2 nucleocapsid antibodies and alkaline phosphatase (AP)-conjugated anti-rabbit antibodies. A similar approach was used to assess SARS-CoV-2-neutralizing antibody levels by capturing spike receptor-binding domain (RBD)-specific antibodies utilizing RBD protein-modified magnetic beads and detecting them using AP-conjugated anti-human IgG antibodies. The sensing mechanism for both assays is based on cysteamine etching-induced fluorescence quenching of bovine serum albumin-protected gold nanoclusters where cysteamine is generated in proportion to the amount of either SARS-CoV-2 virus or anti-SARS-CoV-2 receptor-binding domain-specific immunoglobulin antibodies (anti-RBD IgG antibodies). High sensitivity can be achieved in 5 h 15 min for the anti-RBD IgG antibody detection and 6 h 15 min for virus detection, although the assay can be run in "rapid" mode, which takes 1 h 45 min for the anti-RBD IgG antibody detection and 3 h 15 min for the virus. By spiking the anti-RBD IgG antibodies and virus in serum and saliva, we demonstrate that the assay can detect the anti-RBD IgG antibodies with a limit of detection (LOD) of 4.0 and 2.0 ng/mL in serum and saliva, respectively. For the virus, we can achieve an LOD of 8.5 × 10⁵ RNA copies/mL and 8.8 × 10⁵ RNA copies/mL in serum and saliva, respectively. Interestingly, this assay can be easily modified to detect myriad analytes of interest.

Effect of Glycosylation on Self-Assembly of Lipid A Lipopolysaccharides in Aqueous Solutions

Lipopolysaccharides (LPSs) based on lipid A produced by bacteria are of interest due to their bioactivity in stimulating immune responses, as are simpler synthetic components or analogues. Here, the self-assembly in water of two monodisperse lipid A derivatives based on simplified bacterial LPS structures is examined and compared to that of a native Escherichia coli LPS using small-angle X-ray scattering and cryogenic transmission electron microscopy. The critical aggregation concentration is obtained from fluorescence probe experiments, and conformation is probed using circular dichroism spectroscopy. The E. coli LPS is found to form wormlike micelles, whereas the synthetic analogues bearing six lipid chains and with four or two saccharide head groups (Kdo₂-lipid A and monophosphoryl lipid A) self-assemble into nanosheets or vesicles, respectively. These observations are rationalized by considering the surfactant packing parameter.

Preclinical evaluation of immunogenicity, efficacy and safety of a recombinant plant-based SARS-CoV-2 RBD vaccine formulated with 3M-052-Alum adjuvant

Cost-effective, and accessible vaccines are needed for mass immunization to control the ongoing coronavirus disease 2019 (COVID-19), especially in low- and middle-income countries (LMIC).A plant-based vaccine is an attractive technology platform since the recombinant proteins can be easily produced at large scale and low cost. For the recombinant subunit-based vaccines, effective adjuvants are crucial to enhance the magnitude and breadth of immune responses elicited by the vaccine. In this study, we report a preclinical evaluation of the immunogenicity, efficacy and safety of a recombinant plant-based SARS-CoV-2 RBD vaccine formulated with 3M-052 (TLR7/8 agonist)-Alum adjuvant. This vaccine formulation, named Baiya SARS-CoV-2 Vax 2, induced significant levels of RBD-specific IgG and neutralizing antibody responses in mice. A viral challenge study using humanized K18-hACE2 mice has shown that animals vaccinated with two doses of Baiya SARS-CoV-2 Vax 2 established immune protection against SARS-CoV-2. A study in nonhuman primates (cynomolgus monkeys) indicated that immunization with two doses of Baiya SARS-CoV-2 Vax 2 was safe, well tolerated, and induced neutralizing antibodies against the prototype virus and other viral variants (Alpha, Beta, Gamma, Delta, and Omicron subvariants). The toxicity of Baiya SARS-CoV-2 Vax 2 was further investigated in Jcl:SD rats, which demonstrated that a single dose and repeated doses of Baiya SARS-CoV-2 Vax 2 were well tolerated and no mortality or unanticipated findings were observed. Overall, these preclinical findings support further clinical development of Baiya SARS-CoV-2 Vax 2.

Immunogenicity and efficacy of recombinant subunit SARS-CoV-2 vaccine candidate in the Syrian hamster model

SARS-CoV-2 causes devastating impact on the human population and has become a major public health concern. The frequent emergence of SARS-CoV-2 variants of concern urges the development of safe and efficacious vaccine against SARS-CoV-2 variants. We developed a candidate vaccine Baiya SARS-CoV-2 Vax 1, based on SARS-CoV-2 receptor-binding domain (RBD) by fusing with the Fc region of human IgG. The RBD-Fc fusion was produced in Nicotiana benthamiana. Previously, we reported that this plant-produced vaccine is effective in inducing immune response in both mice and non-human primates. Here, the efficacy of our vaccine candidate was tested in Syrian hamster challenge model. Hamsters immunized with two intramuscular doses of Baiya SARS-CoV-2 Vax 1 induced neutralizing antibodies against SARS-CoV-2 and protected from SARS-CoV-2 challenge with reduced viral load in the lungs. These preliminary results demonstrate the ability of plant-produced subunit vaccine Baiya SARS-CoV-2 Vax 1 to provide protection against SARS-CoV-2 infection in hamsters.

Safety and immunogenicity of a recombinant receptor-binding domain-based protein subunit vaccine (Noora vaccine™) against COVID-19 in adults: A randomized, double-blind, placebo-controlled, Phase 1 trial

The development of a safe and effective vaccine is essential to protect populations against coronavirus disease 2019 (COVID-19). There are several vaccine candidates under investigation with different mechanisms of action. In the present study, we have evaluated the safety and immunogenicity of a recombinant receptor-binding domain (RBD)-based protein subunit vaccine (Noora vaccine) against COVID-19 in adults. This Phase 1 trial is a randomized, double-blind, placebo-controlled study to evaluate the safety and immunogenicity of the recombinant RBD-based protein subunit vaccine (Noora vaccine) against COVID-19 in healthy adults volunteers. Eligible participants were included in this study after evaluating their health status and considering the exclusion criteria. They were then randomized into three groups and received three doses of vaccine (80 µg, 120 µg, and placebo) on Days 0, 21, and 35. Primary outcomes including solicited, unsolicited, and medically attended adverse events were recorded during this study. Secondary outcomes including the humoral and cellular immunity (including anti-RBD IgG antibody and neutralizing antibody) were measured on Days 0, 21, 28, 35, 42, and 49 by using the ELISA kit and the Virus Neutralization Test (VNT) was performed on day 49. Totally 70 cases were included in this Phase 1 trial and 60 of them completed the study. Safety assessments showed no severe adverse events. Local pain at the vaccine injection site occurred in 80% of the vaccinated volunteers. Induration and redness at the injection site were the other adverse reactions of this vaccine. There was no significant difference between the studied groups regarding adverse reactions. Anti-RBD IgG antibody and neutralizing antibody assessment showed significant seroconversion in comparison to the placebo group (80%, and 100% respectively, p < 0.001). The cellular immunity panel also showed mild to moderate induction of TH1 responses and the VNT showed 78% of seroprotection. The results of this Phase 1 trial showed acceptable safety without serious adverse events and significant seroconversions in the humoral and cellular immunity panel. The dose of 80 µg is an appropriate dose for injection in the next phases of the trial.

Antigen-adjuvant interactions, stability, and immunogenicity profiles of a SARS-CoV-2 receptor-binding domain (RBD) antigen formulated with aluminum salt and CpG adjuvants

Low-cost, refrigerator-stable COVID-19 vaccines will facilitate global access and improve vaccine coverage in low- and middle-income countries. To this end, subunit-based approaches targeting the receptor-binding domain (RBD) of SARS-CoV-2 Spike protein remain attractive. Antibodies against RBD neutralize SARS-CoV-2 by blocking viral attachment to the host cell receptor, ACE2. Here, a yeast-produced recombinant RBD antigen (RBD-L452K-F490W or RBD-J) was formulated with various combinations of aluminum-salt (Alhydrogel®, AH; AdjuPhos®, AP) and CpG 1018 adjuvants. We assessed the effect of antigen-adjuvant interactions on the stability and mouse immunogenicity of various RBD-J preparations. While RBD-J was 50% adsorbed to AH and <15% to AP, addition of CpG resulted in complete AH binding, yet no improvement in AP adsorption. ACE2 competition ELISA analyses of formulated RBD-J stored at varying temperatures (4, 25, 37°C) revealed that RBD-J was destabilized by AH, an effect exacerbated by CpG. DSC studies demonstrated that aluminum-salt and CpG adjuvants decrease the conformational stability of RBD-J and suggest a direct CpG-RBD-J interaction. Although AH+CpG-adjuvanted RBD-J was the least stable in vitro, the formulation was most potent at eliciting SARS-CoV-2 pseudovirus neutralizing antibodies in mice. In contrast, RBD-J formulated with AP+CpG showed minimal antigen-adjuvant interactions, a better stability profile, but suboptimal immune responses. Interestingly, the loss of in vivo potency associated with heat-stressed RBD-J formulated with AH+CpG after one dose was abrogated by a booster. Our findings highlight the importance of elucidating the key interrelationships between antigen-adjuvant interactions, storage stability, and in vivo performance to enable successful formulation development of stable and efficacious subunit vaccines.

Glycoconjugates: Synthesis, Functional Studies, and Therapeutic Developments

Glycoconjugates are major constituents of mammalian cells that are formed via covalent conjugation of carbohydrates to other biomolecules like proteins and lipids and often expressed on the cell surfaces. Among the three major classes of glycoconjugates, proteoglycans and glycoproteins contain glycans linked to the protein backbone via amino acid residues such as Asn for N-linked glycans and Ser/Thr for O-linked glycans. In glycolipids, glycans are linked to a lipid component such as glycerol, polyisoprenyl pyrophosphate, fatty acid ester, or sphingolipid. Recently, glycoconjugates have become better structurally defined and biosynthetically understood, especially those associated with human diseases, and are accessible to new drug, diagnostic, and therapeutic developments. This review describes the status and new advances in the biological study and therapeutic applications of natural and synthetic glycoconjugates, including proteoglycans, glycoproteins, and glycolipids. The scope, limitations, and novel methodologies in the synthesis and clinical development of glycoconjugates including vaccines, glyco-remodeled antibodies, glycan-based adjuvants, glycan-specific receptor-mediated drug delivery platforms, etc., and their future prospectus are discussed.

Safety and immunogenicity of a SARS-CoV-2 recombinant protein nanoparticle vaccine (GBP510) adjuvanted with AS03: A randomised, placebo-controlled, observer-blinded phase 1/2 trial

BACKGROUND

Vaccination has helped to mitigate the COVID-19 pandemic. Ten traditional and novel vaccines have been listed by the World Health Organization for emergency use. Additional alternative approaches may better address ongoing vaccination globally, where there remains an inequity in vaccine distribution. GBP510 is a recombinant protein vaccine, which consists of self-assembling, two-component nanoparticles, displaying the receptor-binding domain (RBD) in a highly immunogenic array.

METHODS

This randomised, placebo-controlled, observer-blinded phase 1/2 study was conducted to evaluate the safety and immunogenicity of GBP510 (2-doses at a 28-day interval) adjuvanted with or without AS03 in adults aged 19-85 years at 14 hospital sites in Korea. This study was consisted of two stages (stage I, healthy adults aged 19-55 years; stage II, 240 healthy adults aged 19-85 years). Healthy participants who did not previously receive any vaccine within 4 weeks (2 weeks for flu vaccine) prior to the study, no history of COVID-19 vaccination/medication, and were naïve to SARS-CoV-2 infection at screening were eligible for the study enrollment. Participants were block-randomized in a 2:2:1 ratio to receive 2 doses of 10 µg GBP510 adjuvanted with AS03 (group 1), 10 µg unadjuvanted GBP510 (group 2) or placebo intramuscularly in stage I, while they were block-randomized in a 2:2:1:1 ratio to receive 10 µg GBP510 adjuvanted with AS03 (group 1), 25 µg GBP510 adjuvanted with AS03 (group 3), 25 µg unadjuvanted GBP510 (group 4) or placebo in stage II. The primary safety outcomes were solicited and unsolicited adverse events, while primary immunogenicity outcomes included anti-SARS-CoV-2 RBD IgG antibodies; neutralizing antibody responses; and T-cell immune responses. Safety assessment included all participants who received at least 1 dose of study intervention (safety set). Immunogenicity assessment included all participants who completed the vaccination schedule and had valid immunogenicity assessment results without any major protocol deviations (per-protocol set). This study was registered with ClinicalTrials.gov (NCT04750343).

FINDINGS

Of 328 participants who were enrolled between February 1 and May 28, 2021, 327 participants received at least 1 dose of vaccine. Each received either 10 µg GBP510 adjuvanted with AS03 (Group 1, n = 101), 10 µg unadjuvanted GBP510 (Group 2, n = 10), 25 µg GBP510 adjuvanted with AS03 (Group 3, n = 104), 25 µg unadjuvanted GBP510 (Group 4, n = 51), or placebo (n = 61). Higher reactogenicity was observed in the GBP510 adjuvanted with AS03 groups compared to the non-adjuvanted and placebo groups. The most frequently reported solicited local adverse event (AE) was injection site pain after any vaccination: (88·1% in group 1; 50·0% in group 2; 92·3% in group 3; 66·7% in group 4). Fatigue and myalgia were two most frequently reported systemic AEs and more frequently reported in GBP510 adjuvanted with AS03 recipients (79·2% and 78·2% in group 1; 75·0% and 79·8% in group 3, respectively) than in the unadjuvanted vaccine recipients (40·0% and of 40·0% in group 2; 60·8% and 47·1% in group 4) after any vaccination. Reactogenicity was higher post-dose 2 compared to post-dose 1, particularly for systemic AEs. The geometric mean concentrations of anti-SARS-CoV-2-RBD IgG antibody reached 2163·6/2599·2 BAU/mL in GBP510 adjuvanted with AS03 recipients (10 µg/25 µg) by 14 days after the second dose. Two-dose vaccination of 10 µg or 25 µg GBP510 adjuvanted with AS03 induced high titres of neutralizing antibody via pseudovirus (1369·0/1431·5 IU/mL) and wild-type virus (949·8/861·0 IU/mL) assay.

INTERPRETATION

GBP510 adjuvanted with AS03 was well tolerated and highly immunogenic. These results support further development of the vaccine candidate, which is currently being evaluated in Phase 3.

FUNDING

This work was supported, in whole or in part, by funding from CEPI and the Bill & Melinda Gates Foundation Investment ID OPP1148601. The Bill & Melinda Gates Foundation supported this project for the generation of IND-enabling data and CEPI supported this clinical study.

Intradermal Immunization of SARS-CoV-2 Original Strain Trimeric Spike Protein Associated to CpG and AddaS03 Adjuvants, but Not MPL, Provide Strong Humoral and Cellular Response in Mice

Despite the intramuscular route being the most used vaccination strategy against SARS-CoV-2, the intradermal route has been studied around the globe as a strong candidate for immunization against SARS-CoV-2. Adjuvants have shown to be essential vaccine components that are capable of driving robust immune responses and increasing the vaccination efficacy. In this work, our group aimed to develop a vaccination strategy for SARS-CoV-2 using a trimeric spike protein, by testing the best route with formulations containing the adjuvants AddaS03, CpG, MPL, Alum, or a combination of two of them. Our results showed that formulations that were made with AddaS03 or CpG alone or AddaS03 combined with CpG were able to induce high levels of IgG, IgG1, and IgG2a; high titers of neutralizing antibodies against SARS-CoV-2 original strain; and also induced high hypersensitivity during the challenge with Spike protein and a high level of IFN-γ producing CD4+ T-cells in mice. Altogether, those data indicate that AddaS03, CpG, or both combined may be used as adjuvants in vaccines for COVID-19.

Using Dual Toll-like Receptor Agonism to Drive Th1-Biased Response in a Squalene- and α-Tocopherol-Containing Emulsion for a More Effective SARS-CoV-2 Vaccine

A diversity of vaccines is necessary to reduce the mortality and morbidity of SARS-CoV-2. Vaccines must be efficacious, easy to manufacture, and stable within the existing cold chain to improve their availability around the world. Recombinant protein subunit vaccines adjuvanted with squalene-based emulsions such as AS03™ and MF59™ have a long and robust history of safe, efficacious use with straightforward production and distribution. Here, subunit vaccines were made with squalene-based emulsions containing novel, synthetic toll-like receptor (TLR) agonists, INI-2002 (TLR4 agonist) and INI-4001 (TLR7/8 agonist), using the recombinant receptor-binding domain (RBD) of SARS-CoV-2 S protein as an antigen. The addition of the TLR4 and TLR7/8 agonists, alone or in combination, maintained the formulation characteristics of squalene-based emulsions, including a sterile filterable droplet size (<220 nm), high homogeneity, and colloidal stability after months of storage at 4, 25, and 40 °C. Furthermore, the addition of the TLR agonists skewed the immune response from Th2 towards Th1 in immunized C57BL/6 mice, resulting in an increased production of IgG2c antibodies and a lower antigen-specific production of IL-5 with a higher production of IFNγ by lymphocytes. As such, incorporating TLR4 and TLR7/8 agonists into emulsions leveraged the desirable formulation and stability characteristics of emulsions and can induce Th1-type humoral and cell-mediated immune responses to combat the continued threat of SARS-CoV-2.

An RBD-Based Diagnostic Method Useful for the Surveillance of Protective Immunity against SARS-CoV-2 in the Population

After more than two years, the COVID-19 pandemic is still ongoing and evolving all over the world; human herd immunity against SARS-CoV-2 increases either by infection or by unprecedented mass vaccination. A substantial change in population immunity is expected to contribute to the control of transmission. It is essential to monitor the extension and duration of the population's immunity to support the decisions of health authorities in each region and country, directed to chart the progressive return to normality. For this purpose, the availability of simple and cheap methods to monitor the levels of relevant antibodies in the population is a widespread necessity. Here, we describe the development of an RBD-based ELISA for the detection of specific antibodies in large numbers of samples. The recombinant expression of an RBD-poly-His fragment was carried out using either bacterial or eukaryotic cells in in vitro culture. After affinity chromatography purification, the performance of both recombinant products was compared by ELISA in similar trials. Our results showed that eukaryotic RBD increased the sensitivity of the assay. Interestingly, our results also support a correlation of the eukaryotic RBD-based ELISA with other assays aimed to test for neutralizing antibodies, which suggests that it provides an indication of protective immunity against SARS-CoV-2.

Experimental veterinary SARS-CoV-2 vaccine cross neutralization of the Delta (B.1.617.2) variant virus in cats

SARS-CoV-2 has exhibited varying pathogenesis in a variety of Mammalia family's including Canidae, Mustelidae, Hominidae, Cervidae, Hyaenidae, and Felidae. Novel SARS-CoV-2 variants characterized by spike protein mutations have recently resulted in clinical and epidemiological concerns, as they potentially have increased infectious rates, increased transmission, or reduced neutralization by antibodies produced via vaccination. Many variants have been identified at this time, but the variant of continuing concern has been the Delta variant (B.1.617.2), due to its increased transmissibility and infectious rate. Felines vaccinated using an experimental SARS-CoV-2 spike protein-based veterinary vaccine mounted a robust immune response to the SARS-CoV-2 spike protein. Using a reporter virus particle system and feline serum, we have verified that vaccinated felines produce antibodies that neutralize the SARS-CoV-2 Wuhan strain and variant B.1.617.2 at comparable levels.

Alum Adjuvant and Built-in TLR7 Agonist Synergistically Enhance Anti-MUC1 Immune Responses for Cancer Vaccine

The tumor-associated antigen mucin 1 (MUC1) is an attractive target of antitumor vaccine, but its weak immunogenicity is a big challenge for the development of vaccine. In order to enhance immune responses against MUC1, herein, we conjugated small molecular toll-like receptor 7 agonist (TLR7a) to carrier protein BSA via MUC1 glycopeptide to form a three-component conjugate (BSA-MUC1-TLR7a). Furthermore, we combined the three-component conjugate with Alum adjuvant to explore their synergistic effects. The immunological studies indicated that Alum adjuvant and built-in TLR7a synergistically enhanced anti-MUC1 antibody responses and showed Th1-biased immune responses. Meanwhile, antibodies elicited by the vaccine candidate effectively recognized tumor cells and induced complement-dependent cytotoxicity. In addition, Alum adjuvant and built-in TLR7a synergistically enhanced MUC1 glycopeptide-specific memory CD8+ T-cell immune responses. More importantly, the vaccine with the binary adjuvant can significantly inhibit tumor growth and prolong the survival time of mice in the tumor challenge experiment. This novel vaccine construct provides an effective strategy to develop antitumor vaccines.

A Novel Bacterial Protease Inhibitor Adjuvant in RBD-Based COVID-19 Vaccine Formulations Containing Alum Increases Neutralizing Antibodies, Specific Germinal Center B Cells and Confers Protection Against SARS-CoV-2 Infection in Mice

In this work, we evaluated recombinant receptor binding domain (RBD)-based vaccine formulation prototypes with potential for further clinical development. We assessed different formulations containing RBD plus alum, AddaS03, AddaVax, or the combination of alum and U-Omp19: a novel Brucella spp. protease inhibitor vaccine adjuvant. Results show that the vaccine formulation composed of U-Omp19 and alum as adjuvants has a better performance: it significantly increased mucosal and systemic neutralizing antibodies in comparison to antigen plus alum, AddaVax, or AddaS03. Antibodies induced with the formulation containing U-Omp19 and alum not only increased their neutralization capacity against the ancestral virus but also cross-neutralized alpha, lambda, and gamma variants with similar potency. Furthermore, the addition of U-Omp19 to alum vaccine formulation increased the frequency of RBD-specific geminal center B cells and plasmablasts. Additionally, U-Omp19+alum formulation induced RBD-specific Th1 and CD8⁺ T-cell responses in spleens and lungs. Finally, this vaccine formulation conferred protection against an intranasal severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) challenge of K18-hACE2 mice.

SARS-CoV-2 Vaccination boosts Neutralizing Activity against Seasonal Human Coronaviruses

Background

Most of the millions of people that are vaccinated against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of coronavirus disease 2019 (COVID-19), have previously been infected by related circulating human coronaviruses (hCoVs) causing common colds and will experience further encounters with these viruses in the future. Whether COVID-19 vaccinations impact neutralization of seasonal coronaviruses is largely unknown.

Methods

We analyzed the capacity of sera derived from 24 individuals before and after heterologous ChAdOx1 nCoV-19 BNT162b2 prime-boost vaccination to neutralize genuine OC43, NL63, and 229E hCoVs, as well as viral pseudoparticles carrying the SARS-CoV-1, SARS-CoV-2, Middle East Respiratory Syndrome (MERS)-CoV, and hCoV-OC43, hCoV-NL63, and hCoV-229E spike proteins. Genuine hCoVs or spike containing pseudovirions were incubated with different concentrations of sera and neutralization efficiencies were determined by measuring viral RNA yields, intracellular viral nucleocapsid expression, or reporter gene expression in Huh-7 cells.

Results

All individuals showed strong preexisting immunity against hCoV-OC43. Neutralization of hCoV-NL63 was more variable and all sera showed only modest inhibitory activity against genuine hCoV-229E. SARS-CoV-2 vaccination resulted in efficient cross-neutralization of SARS-CoV-1 but not of MERS-CoV. On average, vaccination significantly increased the neutralizing activity against genuine hCoV-OC43, hCoV-NL63, and hCoV-229E.

Conclusions

Heterologous COVID-19 vaccination may confer some cross-protection against endemic seasonal coronaviruses.