Adjuvants for COVID-19 Vaccines

Role of NLRP3 inflammasome in nanoparticle adjuvant-mediated immune response

The nucleotide-binding oligomerization domain (NOD)-like receptor (NLR) family pyrin domain-containing 3 (NLRP3) inflammasome is pivotal in orchestrating the immune response induced by nanoparticle adjuvants. Understanding the intricate mechanisms underlying the activation of NLRP3 inflammasome by these adjuvants is crucial for deciphering their immunomodulatory properties. This review explores the involvement of the NLRP3 inflammasome in mediating immune responses triggered by nanoparticle adjuvants. It delves into the signaling pathways and cellular mechanisms involved in NLRP3 activation, highlighting its significance in modulating the efficacy and safety of nanoparticle-based adjuvants. A comprehensive grasp of the interplay between NLRP3 inflammasome and nanoparticle adjuvants holds promise for optimizing vaccine design and advancing immunotherapeutic strategies.

Immuno-Microbial Signature of Vaccine-Induced Immunity against SARS-CoV-2

Although vaccines address critical public health needs, inter-individual differences in responses are not always considered in their development. Understanding the underlying basis for these differences is needed to optimize vaccine effectiveness and ultimately improve disease control. In this pilot study, pre- and post-antiviral immunological and gut microbiota features were characterized to examine inter-individual differences in SARS-CoV-2 mRNA vaccine response. Blood and stool samples were collected before administration of the vaccine and at 2-to-4-week intervals after the first dose. A cohort of 14 adults was separated post hoc into two groups based on neutralizing antibody levels (high [HN] or low [LN]) at 10 weeks following vaccination. Bivariate correlation analysis was performed to examine associations between gut microbiota, inflammation, and neutralization capacity at that timepoint. These analyses revealed significant differences in gut microbiome composition and inflammation states pre-vaccination, which predicted later viral neutralization capacity, with certain bacterial taxa, such as those in the genus Prevotella, found at higher abundance in the LN vs HN group that were also negatively correlated with a panel of inflammatory factors such as IL-17, yet positively correlated with plasma levels of the high mobility group box 1 (HMGB-1) protein at pre-vaccination. In particular, we observed a significant inverse relationship (Pearson = -0.54, p = 0.03) between HMGB-1 pre-vaccination and neutralization capacity at 10 weeks post-vaccination. Consistent with known roles as mediators of inflammation, our results altogether implicate HMGB-1 and related gut microbial signatures as potential biomarkers in predicting SARS-CoV-2 mRNA vaccine effectiveness measured by the production of viral neutralization antibodies.

Safe plant Hsp90 adjuvants elicit an effective immune response against SARS-CoV2-derived RBD antigen

To better understand the role of pHsp90 adjuvant in immune response modulation, we proposed the use of the Receptor Binding Domain (RBD) of the Spike protein of SARS-CoV2, the principal candidate in the design of subunit vaccines. We evaluated the humoral and cellular immune responses against RBD through the strategy "protein mixture" (Adjuvant + Antigen). The rRBD adjuvanted with rAtHsp81.2 group showed a higher increase of the anti-rRBD IgG1, while the rRBD adjuvanted with rNbHsp90.3 group showed a significant increase in anti-rRBD IgG2b/2a. These results were consistent with the cellular immune response analysis. Spleen cell cultures from rRBD + rNbHsp90.3-immunized mice showed significantly increased IFN-γ production. In contrast, spleen cell cultures from rRBD + rAtHsp81.2-immunized mice showed significantly increased IL-4 levels. Finally, vaccines adjuvanted with rNbHsp90.3 induced higher neutralizing antibody responses compared to those adjuvanted with rAtHsp81.2. To know whether both chaperones must form complexes to generate an effective immune response, we performed co-immunoprecipitation (co-IP) assays. The results indicated that the greater neutralizing capacity observed in the rRBD adjuvanted with rNbHsp90.3 group would be given by the rRBD-rNbHsp90.3 interaction rather than by the quality of the immune response triggered by the adjuvants. These results, together with our previous results, provide a comparative benchmark of these two novel and safe vaccine adjuvants for their capacity to stimulate immunity to a subunit vaccine, demonstrating the capacity of adjuvanted SARS-CoV2 subunit vaccines. Furthermore, these results revealed differences in the ability to modulate the immune response between these two pHsp90s, highlighting the importance of adjuvant selection for future rational vaccine and adjuvant design.

Current Progress, Challenges and Prospects in the Development of COVID-19 Vaccines

The COVID-19 pandemic has resulted in over 772 million confirmed cases, including nearly 7 million deaths, according to the World Health Organization (WHO). Leveraging rapid development, accelerated vaccine approval processes, and large-scale production of various COVID-19 vaccines using different technical platforms, the WHO declared an end to the global health emergency of COVID-19 on May 5, 2023. Current COVID-19 vaccines encompass inactivated, live attenuated, viral vector, protein subunit, nucleic acid (DNA and RNA), and virus-like particle (VLP) vaccines. However, the efficacy of these vaccines is diminishing due to the constant mutation of SARS-CoV-2 and the heightened immune evasion abilities of emerging variants. This review examines the impact of the COVID-19 pandemic, the biological characteristics of the virus, and its diverse variants. Moreover, the review underscores the effectiveness, advantages, and disadvantages of authorized COVID-19 vaccines. Additionally, it analyzes the challenges, strategies, and future prospects of developing a safe, broad-spectrum vaccine that confers sufficient and sustainable immune protection against new variants of SARS-CoV-2. These discussions not only offer insight for the development of next-generation COVID-19 vaccines but also summarize experiences for combating future emerging viruses.

Flublok Quadrivalent Vaccine Adjuvanted with R-DOTAP Elicits a Robust and Multifunctional CD4 T Cell Response That Is of Greater Magnitude and Functional Diversity Than Conventional Adjuvant Systems

It is clear that new approaches are needed to promote broadly protective immunity to viral pathogens, particularly those that are prone to mutation and escape from antibody-mediated immunity. CD4+ T cells, known to target many viral proteins and highly conserved peptide epitopes, can contribute greatly to protective immunity through multiple mechanisms. Despite this potential, CD4+ T cells are often poorly recruited by current vaccine strategies. Here, we have analyzed a promising new adjuvant (R-DOTAP), as well as conventional adjuvant systems AddaVax with or without an added TLR9 agonist CpG, to promote CD4+ T cell responses to the licensed vaccine Flublok containing H1, H3, and HA-B proteins. Our studies, using a preclinical mouse model of vaccination, revealed that the addition of R-DOTAP to Flublok dramatically enhances the magnitude and functionality of CD4+ T cells specific for HA-derived CD4+ T cell epitopes, far outperforming conventional adjuvant systems based on cytokine EliSpot assays and multiparameter flow cytometry. The elicited CD4+ T cells specific for HA-derived epitopes produce IL-2, IFN-γ, IL-4/5, and granzyme B and have multifunctional potential. Hence, R-DOTAP, which has been verified safe by human studies, can offer exciting opportunities as an immune stimulant for next-generation prophylactic recombinant protein-based vaccines.

Efficacy of adjuvant-associated COVID-19 vaccines against SARS-CoV-2 variants of concern in randomized controlled trials: A systematic review and meta-analysis

BACKGROUND

Adjuvants may enhance the efficacy of vaccines. however, the efficacy of adjuvant-associated COVID-19 vaccines (ACVs) remains unclear since the emergence of the COVID-19 pandemic. This study aimed to address this gap by conducting a systematic review and meta-analysis of the efficacy of ACVs against Severe Acute Respiratory Syndrome Coronavirus 2 CoV (SARS-CoV-2) variants of concern (VOC).

METHODS

A systematic search was conducted of randomized controlled trials (RCTs) evaluating the vaccine efficacy (VE) of ACVs against VOC (alpha, beta, gamma, delta, or Omicron), up to May 27, 2023. The DerSimonian-Laird random-effects model was used to assess VE with 95% confidence intervals (CI) through meta-analysis. Cochrane Risk of Bias tools were used to assess the risk of bias in RCTs.

RESULTS

Eight RCTs with 113,202 participants were included in the analysis, which incorporated 4 ACVs [Matrix-M (NVX-CoV2373), Alum (BBV152), CpG-1018/Alum (SCB-2019), and AS03 (CoVLP]). The pooled efficacy of full vaccination with ACVs against VOC was 88.0% (95% CI: 83.0-91.5). Full vaccination was effective against Alpha, Beta, Delta, and Gamma variants, with VE values of 93.66% (95% CI: 86.5-100.74), 64.70% (95% CI: 41.87-87.54), 75.95% (95% CI: 67.9-83.99), and 91.26% (95% CI: 84.35-98.17), respectively. Currently, there is a lack of RCT evidence regarding the efficacy of ACVs against the Omicron variant.

CONCLUSION

In this meta-analysis, it should be that full vaccination with ACVs has high efficacy against Alpha or Gamma variants and moderate efficacy against Beta and Delta variants. Notably, with the exception of the aluminum-adjuvanted vaccine, the other ACVs had moderate to high efficacy against the SARS-CoV-2 variant. This raises concerns about the effectiveness of ACVs booster vaccinations against Omicron.

Adjuvants in COVID-19 vaccines: innocent bystanders or culpable abettors for stirring up COVID-heart syndrome

COVID-19 infection is a multi-system clinical disorder that was associated with increased morbidity and mortality. Even though antiviral therapies such as Remdesvir offered modest efficacy in reducing the mortality and morbidity, they were not efficacious in reducing the risk of future infections. So, FDA approved COVID-19 vaccines which are widely administered in the general population worldwide. These COVID-19 vaccines offered a safety net against future infections and re-infections. Most of these vaccines contain inactivated virus or spike protein mRNA that are primarily responsible for inducing innate and adaptive immunity. These vaccines were also formulated to contain supplementary adjuvants that are beneficial in boosting the immune response. During the pandemic, clinicians all over the world witnessed an uprise in the incidence and prevalence of cardiovascular diseases (COVID-Heart Syndrome) in patients with and without cardiovascular risk factors. Clinical researchers were not certain about the underlying reason for the upsurge of cardiovascular disorders with some blaming them on COVID-19 infections while others blaming them on COVID-19 vaccines. Based on the literature review, we hypothesize that adjuvants included in the COVID-19 vaccines are the real culprits for causation of cardiovascular disorders. Operation of various pathological signaling events under the influence of these adjuvants including autoimmunity, bystander effect, direct toxicity, anti-phospholipid syndrome (APS), anaphylaxis, hypersensitivity, genetic susceptibility, epitope spreading, and anti-idiotypic antibodies were partially responsible for stirring up the onset of cardiovascular disorders. With these mechanisms in place, a minor contribution from COVID-19 virus itself cannot be ruled out. With that being said, we strongly advocate for careful selection of vaccine adjuvants included in COVID-19 vaccines so that future adverse cardiac disorders can be averted.

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.