Covax-19/Spikogen® vaccine based on recombinant spike protein extracellular domain with Advax-CpG55.2 adjuvant provides single dose protection against SARS-CoV-2 infection in hamsters

Enhanced Humoral and Cellular Immune Responses Elicited by Salmonella Flagellin-Adjuvanted SARS-CoV-2 S1 Subunit Vaccine

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes COVID-19, has been spreading and changing globally. Adjuvant-based vaccines can improve vaccine protection by enhancing the immune response. Bacterial flagellin is a potent adjuvant and promotes protective immune responses. Here, we successfully expressed and purified the S1 subunit of SARS-CoV-2. The adjuvanticity of flagellin (FliC) of Salmonella Typhimurium in mice was determined by combining it with the recombinant S1 subunit vaccine. FliC-adjuvanted S1 vaccine could induce significantly enhanced S1-specific Immunoglobulin G (IgG), IgG1 and IgG2a titers, SARS-CoV-2-neutralizing antibodies, and levels of Th1 type (TNF-α and IFN-γ) and Th2 type (Interleukin-5 (IL-5), IL-4, IL-10, and IL-13) cytokines in splenocytes compared with the S1 alone group. Additionally, the titers of S1-specific IgG antibodies in the FliC adjuvant group could maintain a high level for at least 2 months. These results indicated that the FliC-adjuvanted S1 subunit vaccine could trigger strong humoral and cellular immune responses, which could promote the ongoing development of COVID-19 vaccines.

Immunogenicity and safety study of a single dose of SpikoGen® vaccine as a heterologous or homologous intramuscular booster following a primary course of mRNA, adenoviral vector or recombinant protein COVID-19 vaccine in ambulatory adults

BACKGROUND

SpikoGen® is a subunit recombinant Wuhan spike protein produced in insect cells and formulated with Advax-CpG55.2™ adjuvant. It is approved for adult and pediatric use in the Middle East. This study tested the safety and immunogenicity of SpikoGen® as a 3rd, 4th or 5th dose booster following a primary immunisation course of mRNA, adenovirus or SpikoGen® vaccine.

METHODS

The trial recruited participants who had received a previous doses of COVID-19 vaccine more than 3 months prior. Each received a single intramuscular booster dose of SpikoGen® vaccine. Spike and nuclear protein antibody levels were measured at 1 and 3 months post-booster, together with collection of data on SARS-CoV-2 breakthrough infections and symptoms of long COVID.

RESULTS

One-month post-booster, anti-spike IgG, sVNT, and pVNT levels were increased in all groups and there was ∼4-fold neutralizing antibodies against the heterologous Omicron BA.2 and BA.4/5 strains. The SpikoGen®-prime group had the highest levels of anti-spike IgG3, consistent with the Advax-CpG adjuvant driving IgG3 induction. There was no effect of age on the vaccine response. The booster dose was well tolerated with no vaccine-associated serious adverse events. Nine participants (9/74, 12.2 %) had a breakthrough SARS-CoV-2 infection between 2 weeks and 3 months post-booster. No long COVID was observed after breakthrough infections. Breakthrough infection was negatively correlated with baseline anti-nuclear protein IgG seropositivity.

CONCLUSION

A single SpikoGen® booster was well tolerated and stimulated cross- antibody responses against Omicron variants, regardless of the primary vaccine course received. With SARS-CoV-2 variants continuing to evolve, ongoing research is needed into optimum booster strategies.

CLINICALTRIALS

gov registration. NCT05542862.

Immunobiology and immunotherapy of COVID-19

The SARS-CoV-2 outbreak in late 2019 triggered a major increase in activities related to immunobiology and immunotherapy to cope with and find solutions to end the COVID-19 pandemic. The unprecedented approach to research and development of drugs and vaccines against SARS-CoV-2 has substantially improved the understanding of immunobiology for COVID-19, which can also be applied to other infectious diseases. Major efforts were dedicated to the repurposing of existing antiviral drugs and the development of novel ones. For this reason, numerous approaches to evaluating interferons, immunoglobulins, and cytokine inhibitors have been conducted. Antibody-based therapies, especially employing monoclonal antibodies have also been on the agenda. Cell-based therapies involving dendritic cells, macrophages, and CAR T-cell approaches have been evaluated. Many existing antiviral drugs have been repurposed for COVID-19 and novel formulations have been tested. The extraordinarily rapid development of efficient vaccines led to the breakthrough of novel vaccine approaches such as mRNA-based vaccines saving millions of lives. Waning immunity of existing vaccines and emerging SARS-CoV-2 variants have required additional booster vaccinations and re-engineering of new versions of COVID-19 vaccines.

Clinical development of SpikoGen®, an Advax-CpG55.2 adjuvanted recombinant spike protein vaccine

Recombinant protein vaccines represent a well-established, reliable and safe approach for pandemic vaccination. SpikoGen® is a recombinant spike protein trimer manufactured in insect cells and formulated with Advax-CpG55.2 adjuvant. In murine, hamster, ferret and non-human primate studies, SpikoGen® consistently provided protection against a range of SARS-CoV-2 variants. A pivotal Phase 3 placebo-controlled efficacy trial involving 16,876 participants confirmed the ability of SpikoGen® to prevent infection and severe disease caused by the virulent Delta strain. SpikoGen® subsequently received a marketing authorization from the Iranian FDA in early October 2021 for prevention of COVID-19 in adults. Following a successful pediatric study, its approval was extended to children 5 years and older. Eight million doses of SpikoGen® have been delivered, and a next-generation booster version is currently in development. This highlights the benefits of adjuvanted protein-based approaches which should not overlook when vaccine platforms are being selected for future pandemics.

Simplified scalable synthesis of a water-soluble toll-like receptor 2 agonistic lipopeptide adjuvant for use with protein-based viral vaccines

Toll-like receptors (TLRs) form a key bridge between the innate and adaptive immune systems. The lipopeptide based TLR2 agonists such as Pam2CSK4 are promising vaccine adjuvants but drawbacks include its surfactant like nature and cumbersome synthesis. Although the TLR2 activity of Pam2CS-OMe is commensurate with Pam2CSK4, its water solubility is much less, rendering it ineffective for clinical use. In the present investigation, we designed a synthesis pathway for a novel water-soluble TLR2-active analogue, Pam2CS-DMAPA (13), which enhanced the immunogenicity of recombinant SARS-CoV2 and hepatitis B antigens in mice. Co-formulation of compound 13 with 2 % aluminium hydroxide gel led to a further significant improvement in vaccine immunogenicity. This synthetically simpler compound 13 was water soluble and equally potent to Pam2CSK4 adjuvant, but was superior in terms of manufacturing simplicity and scalability. This makes compound 13 a promising TLR2 targeted adjuvant for further development.

Progress in the development of an Advax-adjuvanted protein capsular matrix vaccine against typhoid fever

Typhoid fever, caused by Salmonella Typhi, remains a significant global public health concern, with an estimated 11 - 20 million cases annually. Vaccines are critical to controlling typhoid fever. Widespread vaccination diminishes the emergence of antibiotic-resistant strains of S. Typhi. The economic benefits of vaccination are also substantial, as the costs of treating typhoid fever and its complications can be significant. Ty21a®, a killed whole-cell vaccine, and Vivotif®, a live-attenuated vaccine, have been available for decades but have relatively short durations of action and only provide partial protection. Vi polysaccharide-conjugate vaccines have improved the durability of protection, but there is still room for improvement. Typhax™, a novel alternative to traditional conjugate vaccines, utilizes Vi polysaccharide that is non-covalently entrapped in a poly-L-lysine and CRM197 protein matrix crosslinked by glutaraldehyde. When formulated with Advax-CpG™ adjuvant, Typhax demonstrated promising results in a range of animal models including mice, rabbits, and non-human primates in which it induces high and sustained serum anti-Vi immunoglobulin G and serum bactericidal activity, without any safety or reactogenicity issues. This novel vaccine approach offers the potential for a low-cost, more effective, and durable vaccine against typhoid fever, avoiding the need for frequent booster doses.

Effect of SpikoGen subunit vaccine administration during pregnancy on fetal development of rats

Purpose

The effects of coronavirus disease 2019 vaccination on fertility and pregnancy have turned out to be a main topic of public attention. Inactivated or recombinant protein vaccines are a reliable and safe method but mostly suffer from weak immunogenicity just in case formulated with a suitable adjuvant. The purpose of this research was to assess the impacts of new SpikoGen subunit vaccine administration during pregnancy on organogenesis in the rat fetus, which is a novel achievement in teratogenesis studies.

Materials and Methods

In the first group (G1) animals received normal saline. A dose of 25 µg of the vaccine was administered to groups of rats as follows: groups 2, 3, 4, and 5 received two doses of vaccine on different days before and after start of pregnancy. On day 21, after the caesarean process, the effects of the vaccine were estimated by morphological, skeletal, and histological studies.

Results

Administration of the SpikoGen vaccine had no significant effect on weight, head diameter, tail length, and length of the fetuses to their tail. There were no malformations, toes and legs were fully developed, and all internal organs of the fetus were completely formed. Also, there was no difference in the overall skeletal opacity and density between the control and treatment groups.

Conclusion

The results of this study indicated no negative impacts of the vaccine administration during pregnancy on developing of fetuses in rats.

Effects of age and gender on immunogenicity and reactogenicity of SpikoGen recombinant spike protein vaccine: a post-hoc analysis

SpikoGen® COVID-19 vaccine is based on the spike protein extracellular domain of the ancestral Wuhan-Hu-1 strain modified by removal of the furin cleavage site and addition of stabilising mutations expressed as a recombinant protein in insect cells. It is formulated with Advax-CpG55.2™ adjuvant to ensure optimal immunogenicity. In this study, data from several SpikoGen® clinical trials was retrospectively analysed to assess for any effect of gender or age on seroconversion, neutralizing antibody levels or the incidence of adverse events. Following the 1st dose, older age was associated with a reduced rate of fatigue (RR 0.97, p < 0.001), headache (RR 0.98, p = 0.034) and myalgia (RR 0.97, p=0.016), following the 2nd dose, the rate of fatigue (RR 0.98, p = 0.017) but following the 3rd dose no effect of age on adverse events was evident. Similarly, following the 1st dose, men reported a 19% lower incidence of fatigue, 36% lower incidence of headache and 28% lower incidence of myalgia when compared to women. Interestingly, there was no relationship between age or gender and serum neutralizing antibody levels, although after each vaccine dose there was a consistent trend to women having a higher seroconversion rate. There was no correlation between neutralizing antibody levels and adverse events. Unlike what is seen with mRNA vaccines, reactogenicity trended lower after each subsequent SpikoGen® dose. Overall, SpikoGen® exhibited positive immunogenicity and low reactogenicity, indicating that a low incidence of adverse events does not equate to poor immunogenicity. SpikoGen® remains a promising protein-based vaccine platform for COVID-19 protection.

Post-Hoc Analysis of Potential Correlates of Protection of a Recombinant SARS-CoV-2 Spike Protein Extracellular Domain Vaccine Formulated with Advax-CpG55.2-Adjuvant

SpikoGen® vaccine is a subunit COVID-19 vaccine composed of an insect cell expressed recombinant spike protein extracellular domain formulated with Advax-CpG55.2™ adjuvant. A randomized double-blind, placebo-controlled Phase II clinical trial was conducted in 400 adult subjects who were randomized 3:1 to receive two intramuscular doses three weeks apart of either SpikoGen® vaccine 25 μg or saline placebo, as previously reported. This study reports a post hoc analysis of the trial data to explore potential immune correlates of SpikoGen® vaccine protection. A range of humoral markers collected pre- and post-vaccination, including spike- and RBD-binding IgG and IgA, surrogate (sVNT), and conventional (cVNT) virus neutralization tests were compared between participants who remained infection-free or got infected over three months of follow-up. From 2 weeks after the second vaccine dose, 21 participants were diagnosed with SARS-CoV-2 infection, 13 (4.2%) in the SpikoGen® group and 8 (9%) in the placebo group. Those in the vaccinated group who experienced breakthrough infections had significantly lower sVNT titers (GMT 5.75 μg/mL, 95% CI; 3.72-8.91) two weeks after the second dose (day 35) than those who did not get infected (GMT 21.06 μg/mL, 95% CI; 16.57-26.76). Conversely, those who did not develop SARS-CoV-2 infection during follow-up had significantly higher baseline sVNT, cVNT, spike-binding IgG and IgA, and RBD-binding IgG, consistent with a past SARS-CoV-2 infection. SpikoGen® further reduced the risk of re-infection (OR 0.29) in baseline seropositive (previously infected) as well as baseline seronegative participants. This indicates that while SpikoGen vaccine is protective in seronegative individuals, those with hybrid immunity have the most robust protection.

Revolutionizing adjuvant development: harnessing AI for next-generation cancer vaccines

With the COVID-19 pandemic, the importance of vaccines has been widely recognized and has led to increased research and development efforts. Vaccines also play a crucial role in cancer treatment by activating the immune system to target and destroy cancer cells. However, enhancing the efficacy of cancer vaccines remains a challenge. Adjuvants, which enhance the immune response to antigens and improve vaccine effectiveness, have faced limitations in recent years, resulting in few novel adjuvants being identified. The advancement of artificial intelligence (AI) technology in drug development has provided a foundation for adjuvant screening and application, leading to a diversification of adjuvants. This article reviews the significant role of tumor vaccines in basic research and clinical treatment and explores the use of AI technology to screen novel adjuvants from databases. The findings of this review offer valuable insights for the development of new adjuvants for next-generation vaccines.

Safety and immunogenicity of an adjuvanted recombinant spike protein-based severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccine, SpikeVet™, in selected Carnivora, Primates and Artiodactyla in Australian zoos

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can infect a broad range of animal species and has been associated with severe disease in some taxa. Few studies have evaluated optimal strategies to mitigate the risk to susceptible zoo animals. This study evaluated the safety and immunogenicity of a protein-based veterinary SARS-CoV-2 vaccine (SpikeVet™) in zoo animals. Two to three doses of SpikeVet™ were administered intramuscularly or subcutaneously 3-4 weeks apart to 354 zoo animals representing 38 species. SpikeVet™ was very well tolerated across all species. Minor adverse effects were observed in 1.69% of animals vaccinated, or 1.04% of vaccine doses administered. Preliminary immunogenicity analyses in representative carnivores (meerkats, lions) and an artiodactylid (domestic goat) showed SpikeVet™-immunized animals developed serum antibodies able to neutralize a range of SARS-CoV-2 variants, including the vaccine-homologous Wuhan and Mu variants, as well as vaccine-heterologous Omicron BA.2 and XBB.1 strains. Prior to vaccination, all eight lions were seropositive for Wuhan strain by surrogate viral neutralization testing, suggesting past infection with SARS-CoV-2 or cross-reactive antibodies generated by another closely related coronavirus. These results from a range of zoo species support the ongoing development of SpikeVet™ as a safe and effective veterinary SARS-CoV-2 vaccine.

Mucosal immunization with dual influenza/COVID-19 single-replication virus vector protects hamsters from SARS-CoV-2 challenge

The COVID-19 pandemic has highlighted the need for mucosal vaccines as breakthrough infections, short-lived immune responses and emergence of new variants have challenged the efficacy provided by the first generation of vaccines against SARS-CoV-2 viruses. M2SR SARS-CoV-2, an M2-deleted single-replication influenza virus vector modified to encode the SARS-CoV-2 receptor binding domain, was evaluated following intranasal delivery in a hamster challenge model for protection against Wuhan SARS-CoV-2. An adjuvanted inactivated SARS-CoV-2 whole virus vaccine administered intramuscularly was also evaluated. The intranasal M2SR SARS-CoV-2 was more effective than the intramuscular adjuvanted inactivated whole virus vaccine in providing protection against SARS-CoV-2 challenge. M2SR SARS-CoV-2 elicited neutralizing serum antibodies against Wuhan and Omicron SARS-CoV-2 viruses in addition to cross-reactive mucosal antibodies. Furthermore, M2SR SARS-CoV-2 generated serum HAI and mucosal antibody responses against influenza similar to an H3N2 M2SR influenza vaccine. The intranasal dual influenza/COVID M2SR SARS-CoV-2 vaccine has the potential to provide protection against both influenza and COVID.

A comprehensive review on immunogen and immune-response proteins of SARS-CoV-2 and their applications in prevention, diagnosis, and treatment of COVID-19

Exposure to severe acute respiratory syndrome-corona virus-2 (SARS-CoV-2) prompts humoral immune responses in the human body. As the auxiliary diagnosis of a current infection, the existence of viral proteins can be checked from specific antibodies (Abs) induced by immunogenic viral proteins. For people with a weakened immune system, Ab treatment can help neutralize viral antigens to resist and treat the disease. On the other hand, highly immunogenic viral proteins can serve as effective markers for detecting prior infections. Additionally, the identification of viral particles or the presence of antibodies may help establish an immune defense against the virus. These immunogenic proteins rather than SARS-CoV-2 can be given to uninfected people as a vaccination to improve their coping ability against COVID-19 through the generation of memory plasma cells. In this work, we review immunogenic and immune-response proteins derived from SARS-CoV-2 with regard to their classification, origin, and diverse applications (e.g., prevention (vaccine development), diagnostic testing, and treatment (via neutralizing Abs)). Finally, advanced immunization strategies against COVID-19 are discussed along with the contemporary circumstances and future challenges.

COVID-19 Vaccines: Where Did We Stand at the End of 2023?

Vaccine development against SARS-CoV-2 has been highly successful in slowing down the COVID-19 pandemic. A wide spectrum of approaches including vaccines based on whole viruses, protein subunits and peptides, viral vectors, and nucleic acids has been developed in parallel. For all types of COVID-19 vaccines, good safety and efficacy have been obtained in both preclinical animal studies and in clinical trials in humans. Moreover, emergency use authorization has been granted for the major types of COVID-19 vaccines. Although high safety has been demonstrated, rare cases of severe adverse events have been detected after global mass vaccinations. Emerging SARS-CoV-2 variants possessing enhanced infectivity have affected vaccine protection efficacy requiring re-design and re-engineering of novel COVID-19 vaccine candidates. Furthermore, insight is given into preparedness against emerging SARS-CoV-2 variants.

Comparative immunogenicity and safety of SpikoGen®, a recombinant SARS-CoV-2 spike protein vaccine in children and young adults: An immuno-bridging clinical trial

BACKGROUND

SpikoGen® is a recombinant subunit spike protein ectodomain vaccine manufactured in insect cells and formulated with the novel polysaccharide-based Advax-CpG55.2 adjuvant. This study aimed to compare the immunogenicity and safety of SpikoGen® vaccine in children, adolescents and young adults.

METHODS

This was a non-randomized, three-arm, open-label, parallel-group, immuno-bridging, non-inferiority trial to compare the immunogenicity and safety of a primary course of two intramuscular doses of SpikoGen® vaccine in children aged 5 to < 12 years, adolescents aged 12 to < 18 years and young adults aged 18 to 40 years. Children 5-12 years received a half dose of 12.5 μg spike protein, whereas the other groups received the full vaccine dose. Vaccine immunogenicity was evaluated via assessment of serum anti-spike and neutralizing antibodies 14 days after the second dose. Solicited adverse events were recorded for 7 days after each vaccination. Safety assessments including serious adverse events were continued through six months after the second dose in children and adolescents.

RESULTS

Two weeks after the second dose, seroconversion rates for neutralizing antibody levels were not significantly different for children (59.50 %), adolescents (52.06 %) and adults (56.01 %). The 95 % confidence interval of the difference in seroconversion rates between children and adults was within the prespecified non-inferiority margin of 10 % (-12 % to 5 %). SpikoGen® vaccine was well tolerated in all age groups with the most common solicited adverse events being injection site pain and fatigue which were generally transient and mild.

CONCLUSION

SpikoGen® vaccine was shown to be safe, well tolerated and immunogenic in children as young as 5 years of age, with non-inferior responses to those seen in adults. The Iranian FDA authorisation of SpikoGen® vaccine is now extended down to 5 years of age.

Advax-CpG55.2-adjuvanted monovalent or trivalent SARS-CoV-2 recombinant spike protein vaccine protects hamsters against heterologous infection with Beta or Delta variants

The ongoing evolution of SARS-CoV-2 variants emphasizes the need for vaccines providing broad cross-protective immunity. This study was undertaken to assess the ability of Advax-CpG55.2 adjuvanted monovalent recombinant spike protein (Wuhan, Beta, Gamma) vaccines or a trivalent formulation to protect hamsters againstBeta or Delta virus infection. The ability of vaccines to block virus transmission to naïve co-housed animals was also assessed. In naïve hosts, the Beta variant induced higher virus loads than the Delta variant, and conversely the Delta variant caused more severe disease and was more likely to be associated with virus transmission. The trivalent vaccine formulation provided the best protection against both Beta and Delta infection and also completely prevented virus transmission. The next best performing vaccine was the original monovalent Wuhan-based vaccine. Notably, hamsters that received the monovalent Gamma spike vaccine had the highest viral loads and clinical disease of all the vaccine groups, a potential signal of antibody dependent-enhancement (ADE). These hamsters were also the most likely to transmit Delta virus to naïve recipients. In murine studies, the Gamma spike vaccine induced the highest total spike protein to RBD IgG ratio and the lowest levels of neutralizing antibody, a context that could predispose to ADE. Overall, the study results confirmed that the current SpikoGen® vaccine based on Wuhan spike protein was still able to protect against clinical disease caused by either the Beta or Delta virus variants but suggested additional protection may be obtained by combining it with extra variant spike proteins to make a multivalent formulation. This study highlights the complexity of optimizing vaccine protection against multiple SARS-CoV-2 variants and stresses the need to continue to pursue new and improved COVID-19 vaccines able to provide robust, long-lasting, and broadly cross-protective immunity against constantly evolving SARS-CoV-2 variants.

An overview of protein-based SARS-CoV-2 vaccines

SARS-CoV-2 resulted in the COVID-19 pandemic which, to date, has resulted in an estimated loss of over 15 million human lives globally and continues to have negative social, and economic implications worldwide. Vaccine platforms that can be quickly updated to counter newly emerging SARS-CoV-2 variants are critical in combating the COVID-19 pandemic. Messenger RNA-based SARS-CoV-2 vaccines can be easily updated and have shown superior efficacy over other vaccine types, yet their high cost, reactogenicity, and stringent need for ultracold storage limit their accessibility. Global access to economic, safe, and effective SARS-CoV-2 vaccines is a critical step toward reducing COVID-19-associated mortality and ending the pandemic. Several protein-based SARS-CoV-2 vaccines targeting the spike protein (or its receptor-binding domain) have demonstrated safety and efficacy in clinical studies. Moreover, protein-based vaccines can be updated to immunize against new virus variants. Protein-based vaccines do not contain live viruses and are safe to use in immunocompromised and elderly populations, and can be optimized to improve the immune outcome in these poorly immunoresponsive individuals by using adjuvants. SARS-CoV-2 shows high genetic variability, similar to other RNA viruses, and protein-based vaccines are an economically feasible vaccine platform that can be used to design new vaccines with durable protective immunity, in addition to expanding the vaccine coverage.

Ability of SpikoGen®, an Advax-CpG adjuvanted recombinant spike protein vaccine, to induce cross-neutralising antibodies against SARS-CoV-2 variants

SpikoGen® vaccine is a subunit COVID-19 vaccine expressed in insect cells comprising recombinant spike protein extracellular domain formulated with Advax-CpG55.2™ adjuvant. A Phase 2 trial was conducted in 400 adult participants randomised 3:1 to receive two intramuscular doses of SpikoGen® vaccine or saline placebo 3 weeks apart. Some Phase 2 trial participants later enrolled in a separate booster study and received a third dose of SpikoGen® vaccine. This stored serum was used to assess the ability of SpikoGen® vaccine to induce cross-neutralising antibodies against SARS-CoV-2 variants of concern. Sera taken at baseline and 2 weeks after the second vaccine dose from baseline seronegative Phase 2 subjects was evaluated using a panel of spike pseudotype lentivirus neutralisation assays for the ability to cross-neutralise a wide range of SARS-CoV-2 variants, including Omicron BA.1, BA.2 and BA.4/5. Stored samples of subjects who participated in both the 2-dose Phase 2 trial and a third dose booster trial 6 months later were also analysed for changes in cross-neutralising antibodies over time and dose. Two weeks after the second dose, sera broadly cross-neutralised most variants of concern, albeit with titres against Omicron variants being ~10-fold lower. While Omicron titres fell to low levels 6 months after the second vaccine dose in most subjects, they showed a ~20-fold rise after the third dose booster, after which there was only a ~2-3-fold difference in neutralisation of Omicron and the ancestral strains. Despite being based on the ancestral Wuhan sequence, after two doses, SpikoGen® vaccine induced broadly cross-neutralising serum antibodies. Titres then reduced over time but were rapidly restored by a third dose booster. This resulted in high neutralisation including against the Omicron variants. This data supports ongoing use of SpikoGen® vaccine for protection against recent SARS-CoV-2 Omicron variants.

Developmental and reproductive safety of Advax-CpG55.2™ adjuvanted COVID-19 and influenza vaccines in mice

SpikoGen® is a recombinant spike protein vaccine against COVID-19 that obtained marketing authorization in the Middle East on October 6th, 2021, becoming the first adjuvanted protein-based COVID-19 vaccine of its type to achieve approval. SpikoGen® vaccine utilizes a unique adjuvant Advax-CpG55.2, which comprises delta inulin and CpG55.2 oligonucleotide, a synthetic human toll-like receptor (TLR)-9 agonist. As part of a safety assessment, developmental and reproductive toxicity (DART) studies were undertaken in mice of Advax-CpG55.2 adjuvanted formulations including SpikoGen®, a H7 hemagglutinin influenza vaccine (rH7HA), the bivalent combination of SpikoGen® and rH7HA, and a next-generation quadrivalent spike protein vaccine. In the first study, vaccines were administered intramuscularly to pregnant dams on gestation days (GD) 6.5 and 12.5, and in the second two doses were given in the pre-mating period with a further two doses during gestation. The doses used in the pregnant mice were 250-1000 times the usual human doses on a weight for weight basis. Strong serum antibody responses with neutralizing activity against the relevant virus were seen in the immunized dams and also at the time of weaning in the sera of their pups, consistent with robust maternal antibody transfer. No adverse effects of any of the vaccine formulations were observed in the immunized dams or their pups. Notably, there were no adverse effects of any of the Advax-CpG55.2 adjuvanted vaccines on female mating performance, fertility, ovarian or uterine parameters, embryo-fetal or postnatal survival, fetal growth, or neurofunctional development. No evidence of antigen interference was observed when SpikoGen® vaccine was mixed and co-administered with influenza hemagglutinin vaccine to pregnant dams. Together with the strong safety profile of SpikoGen® vaccine seen in adults and children in human trials, this DART study data supports the safety of Advax-CpG55.2 adjuvanted COVID-19 and influenza vaccine in women of childbearing potential including during pregnancy.

An Advax-CpG55.2 adjuvanted recombinant hemagglutinin vaccine provides immunity against H7N9 influenza in adult and neonatal mice

There is a major unmet need for strategies to improve the immunogenicity and effectiveness of pandemic influenza vaccines, particularly in poor responder populations such as neonates. Recombinant protein approaches to pandemic influenza offer advantages over more traditional inactivated virus approaches, as they are free of problems such as egg adaptation or need for high level biosecurity containment for manufacture. However, a weakness of recombinant proteins is their low immunogenicity. We asked whether the use of an inulin polysaccharide adjuvant (Advax) alone or combined with a TLR9 agonist (CpG55.2) would enhance the immunogenicity and protection of a recombinant hemagglutinin vaccine against H7N9 influenza (rH7HA), including in neonatal mice. Advax adjuvant induced predominantly IgG1 responses against H7HA, whereas Advax-CpG55.2 adjuvant also induced IgG2a, IgG2b and IgG3 responses, consistent with the TLR9 agonist component inducing a Th1 bias. Advax-CpG55.2 adjuvanted rH7HA induced high serum neutralizing antibody titers in adult mice. In newborns it similarly overcame immune hypo-responsiveness and enhanced serum anti-rH7HA IgG levels in 7-day-old BALB/C and C57BL/6 mice. Immunized adult mice were protected against a lethal H7N9 virus challenge. When formulated with Advax-CpG55.2 adjuvant, greater protection was seen with rH7HA than with inactivated H7 whole virus antigen. Advax-CpG55.2 adjuvanted rH7HA represents a promising influenza vaccine platform for further development.

Soluble SARS-CoV-2 RBD and human ACE2 peptidase domain produced in Drosophila S2 cells show functions evoking virus-cell interface

The interaction between the receptor-binding domain (RBD) of the spike glycoprotein of SARS-CoV-2 and the peptidase domain of the human angiotensin-converting enzyme 2 (ACE2) allows the first specific contact at the virus-cell interface making it the main target of neutralizing antibodies. Here, we show a unique and cost-effective protocol using Drosophila S2 cells to produce both RBD and soluble human ACE2 peptidase domain (shACE2) as thermostable proteins, purified via Strep-tag with yields >40 mg L-1 in a laboratory scale. Furthermore, we demonstrate its binding with KD values in the lower nanomolar range (independently of Strep-tag removal) and its capability to be blocked by serum antibodies in a competition ELISA with Strep-Tactin-HRP as a proof-of-concept. In addition, we assess the capacity of RBD to bind native dimeric ACE2 overexpressed in human cells and its antigen properties with specific serum antibodies. Finally, for completeness, we analyzed RBD microheterogeneity associated with glycosylation and negative charges, with negligible effect on binding either with antibodies or shACE2. Our system represents an accessible and reliable tool for designing in-house surrogate virus neutralization tests (sVNTs), enabling the rapid characterization of neutralizing humoral responses elicited against vaccines or infection, especially in the absence of facilities to conduct virus neutralization tests. Moreover, our biophysical and biochemical characterization of RBD and shACE2 produced in S2 cells lays the groundwork for adapting to different variants of concern (VOCs) to study humoral responses elicited against different VOCs and vaccine formulations.

An intranasal vaccine comprising SARS-CoV-2 spike receptor-binding domain protein entrapped in mannose-conjugated chitosan nanoparticle provides protection in hamsters

We developed a novel intranasal SARS-CoV-2 subunit vaccine called NARUVAX-C19/Nano based on the spike protein receptor-binding domain (RBD) entrapped in mannose-conjugated chitosan nanoparticles (NP). A toll-like receptor 9 agonist, CpG55.2, was also added as an adjuvant to see if this would potentiate the cellular immune response to the NP vaccine. The NP vaccine was assessed for immunogenicity, protective efficacy, and ability to prevent virus transmission from vaccinated animals to naive cage-mates. The results were compared with a RBD protein vaccine mixed with alum adjuvant and administered intramuscularly. BALB/c mice vaccinated twice intranasally with the NP vaccines exhibited secretory IgA and a pronounced Th1-cell response, not seen with the intramuscular alum-adjuvanted RBD vaccine. NP vaccines protected Syrian hamsters against a wild-type SARS-CoV-2 infection challenge as indicated by significant reductions in weight loss, lung viral load and lung pathology. However, despite significantly reduced viral load in the nasal turbinates and oropharyngeal swabs from NP-vaccinated hamsters, virus transmission was not prevented to naïve cage-mates. In conclusion, intranasal RBD-based NP formulations induced mucosal and Th1-cell mediated immune responses in mice and protected Syrian hamsters against SARS-CoV-2 infection but not against viral transmission.

An Advax-CpG55.2™ adjuvanted recombinant spike protein vaccine protects cynomolgus macaques from a homologous SARS-CoV-2 virus challenge

Traditional protein-based vaccine approaches to COVID-19 were overshadowed by the new mRNA and adenoviral vector vaccine approaches which were first to receive marketing authorization. The current study tested for the first time in repurposed aged (median 15.4 years) cynomolgus macaques, a novel Advax-CpG55.2™ adjuvanted recombinant extracellular domain spike protein trimer antigen for immunogenicity, protection and safety. Nine animals received two intramuscular injections 10 days apart of recombinant spike protein (25 μg) with Advax-CpG55.2™ (10 mg/200 μg) and 5 controls received saline injections. Serum antibody levels were followed for 3 months and then the animals were challenged with SARS-CoV-2 virus. Clinical signs, local reactions, body weight, food consumption and antibody levels were monitored till termination on either day 3 or 7 post-infection. Two weeks after the second dose, 8/9 immunized macaques had high serum spike and receptor binding domain binding antibodies that were able to cross-neutralize Alpha (B.1.1.7), Beta (B.1.351), Gamma (P.1), Delta (B.1.617.2) and, to a lesser extent, Omicron variants (B.1.1.529 ). Antibody levels decayed over the subsequent 3 months, and minimal neutralizing antibody was detectable immediately prior to the challenge which used a vaccine-homologous Wuhan-like ancestral virus. Of the nine vaccinated animals, only one 18-year-old female sacrificed at d3 had low levels of lung virus, versus 100 % of the control animals. Four of 5 (80 %) control animals had positive lung staining for SARS-CoV-2 virus versus just 1 of 9 (11 %) in the immunized group. The immunized animals exhibited better maintenance of appetite post-challenge. Neutralizing antibody levels rebounded rapidly in immunized animals, post-challenge. This data supports the benefits of Advax-CpG adjuvanted recombinant spike protein vaccine in protecting against a homologous SARS-CoV-2 infection.

Intranasal Single-Replication Influenza Vector Induces Cross-Reactive Serum and Mucosal Antibodies against SARS-CoV-2 Variants

Current SARS-CoV-2 vaccines provide protection for COVID-19-associated hospitalization and death, but remain inefficient at inhibiting initial infection and transmission. Despite updated booster formulations, breakthrough infections and reinfections from emerging SARS-CoV-2 variants are common. Intranasal vaccination to elicit mucosal immunity at the site of infection can improve the performance of respiratory virus vaccines. We developed SARS-CoV-2 M2SR, a dual SARS-CoV-2 and influenza vaccine candidate, employing our live intranasal M2-deficient single replication (M2SR) influenza vector expressing the receptor binding domain (RBD) of the SARS-CoV-2 Spike protein of the prototype strain, first reported in January 2020. The intranasal vaccination of mice with this dual vaccine elicits both high serum IgG and mucosal IgA titers to RBD. Sera from inoculated mice show that vaccinated mice develop neutralizing SARS-CoV-2 antibody titers against the prototype and Delta virus strains, which are considered to be sufficient to protect against viral infection. Moreover, SARS-CoV-2 M2SR elicited cross-reactive serum and mucosal antibodies to the Omicron BA.4/BA.5 variant. The SARS-CoV-2 M2SR vaccine also maintained strong immune responses to influenza A with high titers of anti H3 serum IgG and hemagglutination inhibition (HAI) antibody titers corresponding to those seen from the control M2SR vector alone. With a proven safety record and robust immunological profile in humans that includes mucosal immunity, the M2SR influenza viral vector expressing key SARS-CoV-2 antigens could provide more efficient protection against influenza and SARS-CoV-2 variants.

Big knowledge visualization of the COVID-19 CIDO ontology evolution

BACKGROUND

The extensive international research for medications and vaccines for the devastating COVID-19 pandemic requires a standard reference ontology. Among the current COVID-19 ontologies, the Coronavirus Infectious Disease Ontology (CIDO) is the largest one. Furthermore, it keeps growing very frequently. Researchers using CIDO as a reference ontology, need a quick update about the content added in a recent release to know how relevant the new concepts are to their research needs. Although CIDO is only a medium size ontology, it is still a large knowledge base posing a challenge for a user interested in obtaining the "big picture" of content changes between releases. Both a theoretical framework and a proper visualization are required to provide such a "big picture".

METHODS

The child-of-based layout of the weighted aggregate partial-area taxonomy summarization network (WAT) provides a "big picture" convenient visualization of the content of an ontology. In this paper we address the "big picture" of content changes between two releases of an ontology. We introduce a new DIFF framework named Diff Weighted Aggregate Taxonomy (DWAT) to display the differences between the WATs of two releases of an ontology. We use a layered approach which consists first of a DWAT of major subjects in CIDO, and then drill down a major subject of interest in the top-level DWAT to obtain a DWAT of secondary subjects and even further refined layers.

RESULTS

A visualization of the Diff Weighted Aggregate Taxonomy is demonstrated on the CIDO ontology. The evolution of CIDO between 2020 and 2022 is demonstrated in two perspectives. Drilling down for a DWAT of secondary subject networks is also demonstrated. We illustrate how the DWAT of CIDO provides insight into its evolution.

CONCLUSIONS

The new Diff Weighted Aggregate Taxonomy enables a layered approach to view the "big picture" of the changes in the content between two releases of an ontology.

Evaluating the efficacy and safety of SpikoGen®, an Advax-CpG55.2-adjuvanted severe acute respiratory syndrome coronavirus 2 spike protein vaccine: a phase 3 randomized placebo-controlled trial

OBJECTIVES

We sought to investigate the efficacy and safety of SpikoGen®, a subunit coronavirus disease 2019 (COVID-19) vaccine composed of a recombinant severe acute respiratory syndrome coronavirus 2 spike protein with Advax-CpG55.2™ adjuvant.

METHODS

This randomized, placebo-controlled, double-blind, phase 3 trial was conducted on 16 876 participants randomized (3:1) to receive two intramuscular doses of SpikoGen® or a saline placebo 21 days apart. The primary outcome was to assess the efficacy of SpikoGen® in preventing symptomatic COVID-19. Secondary outcomes included safety assessments and evaluation of SpikoGen® vaccine's efficacy in preventing severe COVID-19. The study aimed for 147 COVID-19 symptomatic cases.

RESULTS

Overall, 12 657 and 4219 participants were randomized to the SpikoGen® and placebo group and followed for a median of 55 days (interquartile range, 48-60 days) and 51 days (interquartile range, 46-58 days) after 14 days of the second dose, respectively. In the final per-protocol analysis, the number of COVID-19 cases was 247 of 9998 (2.4%) in the SpikoGen® group and 119 of 3069 (3.8%) in the placebo group. This equated to a vaccine efficacy of 43.99% (95% CI, 30.3-55.0%). The efficacy was calculated to be 44.22% (95% CI, 31.13-54.82%) among all participants who received both doses. From 2 weeks after the second dose, 5 of 9998 (0.05%) participants in the SpikoGen® group and 6 of 3069 (0.19%) participants in the placebo group developed severe COVID-19, equating to a vaccine efficacy against severe disease of 77.51% (95% CI, 26.3-93.1%). The SpikoGen® vaccine was well tolerated.

DISCUSSION

A 2-dose regimen of SpikoGen® reduced the rate of COVID-19 and severe disease in the wave of the Delta variant.

Recombinant Protein Vaccines against Human Betacoronaviruses: Strategies, Approaches and Progress

Betacoronaviruses have already troubled humanity more than once. In 2002-2003 and 2012, the SARS-CoV and MERS-CoV, respectively, caused outbreaks of respiratory syndromes with a fatal outcome. The spread of the SARS-CoV-2 coronavirus has become a pandemic. These three coronaviruses belong to the genus Betacoronavirus and have a zoonotic origin. The emergence of new coronavirus infections in the future cannot be ruled out, and vaccination is the main way to prevent the spread of the infection. Previous experience in the development of vaccines against SARS and MERS has helped to develop a number of vaccines against SARS-CoV-2 in a fairly short time. Among them, there are quite a few recombinant protein vaccines, which seem to be very promising in terms of safety, minimization of side effects, storage and transportation conditions. The problem of developing a universal betacoronavirus vaccine is also still relevant. Here, we summarize the information on the designing of vaccines based on recombinant proteins against highly pathogenic human betacoronaviruses SARS-CoV, MERS-CoV and SARS-CoV-2.

In Silico Structure-Based Vaccine Design

Structure-based vaccine design (SBVD) is an important technique in computational vaccine design that uses structural information on a targeted protein to design novel vaccine candidates. This increasing ability to rapidly model structural information on proteins and antibodies has provided the scientific community with many new vaccine targets and novel opportunities for future vaccine discovery. This chapter provides a comprehensive overview of the status of in silico SBVD and discusses the current challenges and limitations. Key strategies in the field of SBVD are exemplified by a case study on design of COVID-19 vaccines targeting SARS-CoV-2 spike protein.

In-depth review of delivery carriers associated with vaccine adjuvants: current status and future perspectives

INTRODUCTION

Vaccines are powerful tools for controlling microbial infections and preventing epidemics. To enhance the immune response to antigens, effective subunit vaccines or mRNA vaccines often require the combination of adjuvants or delivery carriers. In recent years, with the rapid development of immune mechanism research and nanotechnology, various studies based on the optimization of traditional adjuvants or various novel carriers have been intensified, and the construction of vaccine adjuvant delivery systems (VADS) with both adjuvant activity and antigen delivery has become more and more important in vaccine research.

AREAS COVERED

This paper reviews the common types of vaccine adjuvant delivery carriers, classifies the VADS according to their basic carrier types, introduces the current research status and future development trend, and emphasizes the important role of VADS in novel vaccine research.

EXPERT OPINION

As the number of vaccine types increases, conventional aluminum adjuvants show limitations in effectively stimulating cellular immune responses, limiting their use in therapeutic vaccines for intracellular infections or tumors. In contrast, the use of conventional adjuvants as VADS to carry immunostimulatory molecules or deliver antigens can greatly enhance the immune boosting effect of classical adjuvants. A comprehensive understanding of the various delivery vehicles will further facilitate the development of vaccine adjuvant research.

Plant-derived immuno-adjuvants in vaccines formulation: a promising avenue for improving vaccines efficacy against SARS-CoV-2 virus

The SARS-CoV-2 outbreak has posed a plethora of problems for the global healthcare system and socioeconomic burden. Despite valiant efforts to contain the COVID-19 outbreak, the situation has deteriorated to the point that there are no viable preventive therapies to treat this disease. The case count has skyrocketed globally due to the newly evolved variants. Despite vaccination drives, the re-occurrence of recent pandemic waves has reinforced the importance of innovation/utilization of immune-booster to achieve appropriate long-term vaccine protection. Plant-derived immuno-adjuvants, which have multifaceted functions, can impede infections by boosting the immune system. Many previous studies have shown that formulation of vaccines using plant-derived adjuvant results in long-lasting immunity may overcome the natural tendency of coronavirus immunity to wane quickly. Plant polysaccharides, glycosides, and glycoprotein extracts have reportedly been utilized as enticing adjuvants in experimental vaccines, such as Advax, Matrix-M, and Mistletoe lectin, which have been shown to be highly immunogenic and safe. When employed in vaccine formulation, Advax and Matrix-M generate long-lasting antibodies, a balanced robust Th1/Th2 cytokine profile, and the stimulation of cytotoxic T cells. Thus, the use of adjuvants derived from plants may increase the effectiveness of vaccines, resulting in the proper immunological response required to combat COVID-19. A few have been widely used in epidemic outbreaks, including SARS and H1N1 influenza, and their use could also improve the efficacy of COVID-19 vaccines. In this review, the immunological adjuvant properties of plant compounds as well as their potential application in anti-COVID-19 therapy are thoroughly discussed.

Mucosal immunization with a delta-inulin adjuvanted recombinant spike vaccine elicits lung-resident immune memory and protects mice against SARS-CoV-2

Multiple SARS-CoV-2 vaccine candidates have been approved for use and have had a major impact on the COVID-19 pandemic. There remains, however, a significant need for vaccines that are safe, easily transportable and protective against infection, as well as disease. Mucosal vaccination is favored for its ability to induce immune memory at the site of infection, making it appealing for SARS-CoV-2 vaccine strategies. In this study we performed in-depth analysis of the immune responses in mice to a subunit recombinant spike protein vaccine formulated with the delta-inulin adjuvant Advax when administered intratracheally (IT), versus intramuscular delivery (IM). Both routes produced robust neutralizing antibody titers (NAb) and generated sterilizing immunity against SARS-CoV-2. IT delivery, however, produced significantly higher systemic and lung-local NAb that resisted waning up to six months post vaccination, and only IT delivery generated inducible bronchus-associated lymphoid tissue (iBALT), a site of lymphocyte antigen presentation and proliferation. This was coupled with robust and long-lasting lung tissue-resident memory CD4⁺ and CD8⁺ T cells that were not observed in IM-vaccinated mice. This study provides a detailed view of the lung-resident cellular response to IT vaccination against SARS-CoV-2 and demonstrates the importance of delivery site selection in the development of vaccine candidates.

Variants of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) and Vaccine Effectiveness

The incidence and death toll due to SARS-CoV-2 infection varied time-to-time; and depended on several factors, including severity (viral load), immune status, age, gender, vaccination status, and presence of comorbidities. The RNA genome of SARS-CoV-2 has mutated and produced several variants, which were classified by the SARS-CoV-2 Interagency Group (SIG) into four major categories. The first category; “Variant Being Monitored (VBM)”, consists of Alpha (B.1.1.7), Beta (B.1.351), Gamma (P.1), Delta (B.1.617.2), Epsilon (B.1.427, B.1.429), Eta (B.1.525), Iota (B.1.526), Kappa (B.1.617.1), Mu (B.1.621), and Zeta (P.2); the second category; “Variants of Concern” consists of Omicron (B.1.1.529). The third and fourth categories include “Variants of Interest (VOI)”, and “Variants of High Consequence (VOHC)”, respectively, and contain no variants classified currently under these categories. The surge in VBM and VOC poses a significant threat to public health globally as they exhibit altered virulence, transmissibility, diagnostic or therapeutic escape, and the ability to evade the host immune response. Studies have shown that certain mutations increase the infectivity and pathogenicity of the virus as demonstrated in the case of SARS-CoV-2, the Omicron variant. It is reported that the Omicron variant has >60 mutations with at least 30 mutations in the Spike protein (“S” protein) and 15 mutations in the receptor-binding domain (RBD), resulting in rapid attachment to target cells and immune evasion. The spread of VBM and VOCs has affected the actual protective efficacy of the first-generation vaccines (ChAdOx1, Ad26.COV2.S, NVX-CoV2373, BNT162b2). Currently, the data on the effectiveness of existing vaccines against newer variants of SARS-CoV-2 are very scanty; hence additional studies are immediately warranted. To this end, recent studies have initiated investigations to elucidate the structural features of crucial proteins of SARS-CoV-2 variants and their involvement in pathogenesis. In addition, intense research is in progress to develop better preventive and therapeutic strategies to halt the spread of COVID-19 caused by variants. This review summarizes the structure and life cycle of SARS-CoV-2, provides background information on several variants of SARS-CoV-2 and mutations associated with these variants, and reviews recent studies on the safety and efficacy of major vaccines/vaccine candidates approved against SARS-CoV-2, and its variants.

Toll-like receptor (TLR) agonists as a driving force behind next-generation vaccine adjuvants and cancer therapeutics

Until recently, the development of new human adjuvants was held back by a poor understanding of their mechanisms of action. The field was revolutionized by the discovery of the toll-like receptors (TLRs), innate immune receptors that directly or indirectly are responsible for detecting pathogen-associated molecular patterns (PAMPs) and respond to them by activating innate and adaptive immune pathways. Hundreds of ligands targeting various TLRs have since been identified and characterized as vaccine adjuvants. This work has important implications not only for the development of vaccines against infectious diseases but also for immuno-therapies against cancer, allergy, Alzheimer's disease, drug addiction and other diseases. Each TLR has its own specific tissue localization and downstream gene signalling pathways, providing researchers the opportunity to precisely tailor adjuvants with specific immune effects. TLR agonists can be combined with other TLR or alternative adjuvants to create combination adjuvants with synergistic or modulatory effects. This review provides an introduction to the various classes of TLR adjuvants and their respective signalling pathways. It provides an overview of recent advancements in the TLR field in the past 2-3 years and discusses criteria for selecting specific TLR adjuvants based on considerations, such as disease mechanisms and correlates of protection, TLR immune biasing capabilities, route of administration, antigen compatibility, new vaccine technology platforms, and age- and species-specific effects.