Aluminum Adjuvants-'Back to the Future'

Neurotoxic effects of aluminum and manganese: From molecular to clinical effects

The existing data demonstrate that aluminum (Al) and manganese (Mn) possess neurotoxic effects upon overexposure due to induction of neuronal oxidative stress and apoptosis, synaptic dysfunction and neurotransmitter metabolism, neuroinflammation, and cytoskeletal pathology. However, systematic evidence regarding contribution of these metals to development of neurological diseases are lacking. Therefore, in this review we provide a summary of the existing data on contribution of Al and Mn exposure to brain diseases and its symptoms. Causal relations were demonstrated for development of parkinsonism upon exposure to high doses of Mn, whereas Al overload is considered the key contributor to dialysis encephalopathy. Certain studies demonstrate that Al and Mn overexposure is associated with neurodegenerative diseases including Alzheimer's and Parkinson's diseases, as well as neurodevelopmental disorders like autism spectrum disorder (ASD) and attention-deficit/hyperactivity disorder (ADHD). Although laboratory studies demonstrate the potential contribution of Al and Mn to molecular pathogenesis of these diseases, clinical findings supporting the causal role of metals is these pathologies are yet insufficient. Therefore, estimation of the contribution of these metals to neurological disorders is essential for development of more effective early diagnostics and prevention of diseases under exposure to adverse neurological effects of Al and Mn compounds.

DNA nanovaccines derived from ferritin-modified glycogens for targeted delivery to immature dendritic cells and for promotion of Th1 cell differentiation

DNA vaccines have emerged as a powerful approach for advanced cancer therapy. Despite the development of various delivery systems to enhance the immunogenicity of DNA vaccines, many still face challenges such as limited DNA condensation, rapid degradation in vivo and insufficient targeting to lymph nodes (LNs). Synthetic dendrimers with modifiable surfaces exhibit high efficiency in DNA condensation, but their synthesis is extremely complex. This study utilizes cationic glycogen, a natural branched dendrimer-like polymer, as the core structure for efficient DNA condensation and delivery, ensuring good biocompatibility. By connecting ferritin light chain to the glycogen surfaces, active targeting of LNs can be achieved due to its affinity for the SCARA5 receptor on immature dendritic cells (DCs), facilitating vaccine migration to the LNs. In addition, a seperate plasmid encoding adjuvant IL-12 was co-delivered to further boost the immunogenicity of the DNA nanovaccine. In vivo and in vitro experiments confirmed the effective transfection capability of this DNA vaccine, demonstrating promoted DC maturation, increased antigen presentation, and Th1 cell differentiation, resulting in improved anti-tumor efficiency in vivo. This innovative multi-gene co-loaded DNA vaccine offers valuable insights into combined gene therapy and broadens the research horizon on non-viral gene carriers. STATEMENT OF SIGNIFICANCE: The DNA vaccine encounters challenges such as limited DNA condensation, rapid degradation and insufficient targeting to lymph nodes (LNs), resulting in generally weak immunogenicity. In the current study, a novel nanovaccine is developed by connecting ferritin light chain to natural dendrimer glycogen, for simultaneous delivery of dual plasmids. The cationized glycogen provides strong DNA condensation ability, while ensuring excellent stability of the nanovaccine. The presence of ferritin light chain leads to effective targeting of dendritic cells (DCs), facilitating its migration to LNs. Moreover, the plasmid encoding the adjuvant IL-12 is co-incorporated with the antigen plasmid to mitigate the immunosuppression environment. This strategy significantly improves the immunogenicity of DNA vaccines, demonstrating high efficiency in cancer immunotherapy.

Cancer vaccine designed from homologous ferritin-based fusion protein with enhanced DC-T cell crosstalk for durable adaptive immunity against tumors

Peptide vaccines based on tumor antigens face the challenges of rapid clearance of peptides, low immunogenicity, and immune suppressive tumor microenvironment. However, the traditional solution mainly uses exogenous substances as adjuvants or carriers to enhance innate immune responses, but excessive inflammation can damage adaptive immunity. In the current study, we propose a straightforward novel nanovaccine strategy by employing homologous human ferritin light chain for minimized innate immunity and dendritic cell (DC) targeting, the cationic KALA peptide for enhanced cellular uptake, and suppressor of cytokine signaling 1 (SOCS1) siRNA for modulating DC activity. Upon fusing with the KALA peptide, this nanovaccine presents as a novel 40-mer cage structure, with highly enriched antigen peptides of proper size (25 nm) for targeted delivery to lymph nodes. The loading of SOCS1 siRNA onto the KALA peptide promoted DC maturation in tumor environment, leading to a 3-fold increase in antigen presentation compared to alum adjuvant. Moreover, it demonstrates remarkable efficacy in suppressing tumor progression and metastasis, together with prolonged survival. In addition, the nanovaccine stimulates up to 40 % memory T cells, thereby achieving sustained protection against tumor re-challenge. This unprecedented nanovaccine platform can ignite fresh interdisciplinary discussions on interactive strategies for future peptide vaccine development.

Immunological In Vitro Assay for Quantification of Adjuvanted Allergoids

BACKGROUND

Many IgE-mediated allergic disorders can be treated with allergen immunotherapy (AIT). In order to improve safety and efficacy, some AIT products contain allergen extracts which are chemically cross-linked to generate allergoids and are adsorbed to aluminum hydroxide adjuvant. The modification and adsorption impair accessibility of the protein and quantification of the allergoid content.

METHODS

An ELISA-like assay to quantify the allergoid content in adjuvanted grass pollen allergoid AIT products (from here on called: AIT drug products; AIT-DPs) was developed using a fluorescence detection system. The high density of the aluminum hydroxide particles enabled pelleting the antigen complexes by centrifugation. Rabbit anti-grass pollen allergoid sera or a mouse anti-Phl p 5 monoclonal antibody (mAb) was used as the primary antibody. Protein content of the samples was quantified by nitrogen analysis.

RESULTS

High specificity of the primary antibodies was confirmed by isoelectric focusing, gel-electrophoresis, and immunoblotting. Performance of the allergoid content assay was demonstrated in grass pollen AIT-DPs with high specificity and low/absent cross-reactivity with tree pollen or mite AIT-DPs. It was used to confirm batch-to-batch consistency and allergoid content of distinct grass pollen AIT-DPs. Overall, in relation to their total protein content, the allergoid content ranged between 0.8 and 2.1 relative to an in-house reference for all grass pollen AIT-DPs, whereas use of mAb revealed product-specific differences in the Phl p 5 amount. Additionally, the assay detects product alteration by heat stress.

CONCLUSION

The described assay is suitable to quantify the allergoid content and quality of allergoids in complex with aluminum hydroxide. It is suitable for animal-free final product testing in vitro, for example, for batch release to ensure the quality of AIT-DPs.

Aluminum promotes B1 cells to produce IL-10 and impairs adaptive immune system

Aluminum (Al) is a metal existing in the human body, yet the immunotoxicity of Al remains elusive. To investigate the immunotoxicity of Al, C57BL/6 mice were treated with 200 or 800 ppm Al via drinking water for 3 months, and thereafter the adaptive immune system was evaluated. In addition, mouse splenocytes and human peripheral blood mononuclear cells (PBMC) were treated with Al in vitro to assess the impact of Al in vitro. Treatment with Al reduced the production of IgM and IgG in the serum, and the activation of B cells, CD4 T cells and CD8 T cells in the spleen of mice; treatment with Al in vitro suppressed the production of IgM and IgG, and the activation of B cells, CD4 T cells and CD8 T cells in mouse splenocytes and human PBMC. In vitro co-culture assays suggested that the suppressed adaptive immunity was due to B cells modified by Al. In terms of mechanism, a direct action of Al on B1 cells induced the B1 cells to be IL-10-producing cells and thereby suppressed the adaptive immune system, which was critically dependent on the Jak1/3-STAT signaling. This study reveals that Al suppresses the adaptive immunity via induction of IL-10-producing B1 cells.

The immunological and pharmacokinetic evaluation of Lipid-PLGA hybrid nanoparticle-based oxycodone vaccines

The current opioid epidemic is one of the most profound public health crises facing the United States. Despite that it has been under the spotlight for years, available treatments for opioid use disorder (OUD) and overdose are limited to opioid receptor ligands such as the agonist methadone and the overdose reversing drugs such as naloxone. Vaccines are emerging as an alternative strategy to combat OUD and prevent relapse and overdose. Most vaccine candidates consist of a conjugate structure containing the target opioid attached to an immunogenic carrier protein. However, conjugate vaccines have demonstrated some intrinsic shortfalls, such as fast degradation and poor recognition by immune cells. To overcome these challenges, we proposed a lipid-PLGA hybrid nanoparticle (hNP)-based vaccine against oxycodone (OXY), which is one of the most frequently misused opioid analgesics. The hNP-based OXY vaccine exhibited superior immunogenicity and pharmacokinetic efficacy in comparison to its conjugate vaccine counterpart. Specifically, the hNP-based OXY vaccine formulated with subunit keyhole limpet hemocyanin (sKLH) as the carrier protein and aluminum hydroxide (Alum) as the adjuvant (OXY-sKLH-hNP(Alum)) elicited the most potent OXY-specific antibody response in mice. The induced antibodies efficiently bound with OXY molecules in blood and suppressed their entry into the brain. In a following dose-response study, OXY-sKLH-hNP(Alum) equivalent to 60 μg of sKLH was determined to be the most promising OXY vaccine candidate moving forward. This study provides evidence that hybrid nanoparticle-based vaccines may be superior vaccine candidates than conjugate vaccines and will be beneficial in treating those suffering from OUD.

A Self-Adjuvanting Large Pore 2D Covalent Organic Framework as a Vaccine Platform

Vaccines are one of the greatest human achievements in public health, as they help prevent the spread of diseases, reduce illness and death rates, saving thousands of lives with few side effects. Traditional vaccine development is centered around using live attenuated or inactivated pathogens, which is expensive and has resulted in vaccine-associated illnesses. Advancements have led to the development of safer subunit vaccines, which contain recombinant proteins isolated from pathogens. Their short half-life and small size make most subunit vaccines less immunogenic. Here, we introduce a large pore 2D covalent organic framework (COF), PyCOFamide, as a promising solution for an effective subunit platform. Our study demonstrates that simple adsorption of a model antigen, ovalbumin (OVA), onto PyCOFamide (OVA@COF) significantly enhances humoral and cell-mediated immune response compared to free OVA. OVA@COF exhibited heightened immune cell activation and acts as an antigen reservoir, facilitating antigen-presenting cell trafficking to the draining lymph nodes, amplifying the humoral immune response. Additionally, the breakdown of the COF releases monomers that adjuvant the activation of immune cells vital to creating strong immunity. This platform offers a potential avenue for safer, more effective subunit vaccines.

Virus-Mimicking Polymer Nanocomplexes Co-Assembling HCV E1E2 and Core Proteins with TLR 7/8 Agonist-Synthesis, Characterization, and In Vivo Activity

Hepatitis C virus (HCV) is a major public health concern, and the development of an effective HCV vaccine plays an important role in the effort to prevent new infections. Supramolecular co-assembly and co-presentation of the HCV envelope E1E2 heterodimer complex and core protein presents an attractive vaccine design strategy for achieving effective humoral and cellular immunity. With this objective, the two antigens were non-covalently assembled with an immunostimulant (TLR 7/8 agonist) into virus-mimicking polymer nanocomplexes (VMPNs) using a biodegradable synthetic polyphosphazene delivery vehicle. The resulting assemblies were characterized using dynamic light scattering and asymmetric flow field-flow fractionation methods and directly visualized in their vitrified state by cryogenic electron microscopy. The in vivo superiority of VMPNs over the individual components and an Alum-formulated vaccine manifests in higher neutralizing antibody titers, the promotion of a balanced IgG response, and the induction of a cellular immunity-CD4+ T cell responses to core proteins. The aqueous-based spontaneous co-assembly of antigens and immunopotentiating molecules enabled by a synthetic biodegradable carrier offers a simple and effective pathway to the development of polymer-based supramolecular nanovaccine systems.

Cell Wall Protein 2 as a Vaccine Candidate Protects Mice Against Clostridioides difficile Infection

BACKGROUND/OBJECTIVES

Clostridioides difficile is a Gram-positive, spore-forming enteric pathogen that causes intestinal disorders, including inflammation and diarrhea, primarily through toxin production. Standard treatment options for C. difficile infection (CDI) involve a limited selection of antibiotics that are not fully effective, leading to high recurrence rates. Vaccination presents a promising strategy for preventing both CDI and its recurrence. Cell wall protein 2 (Cwp2), a highly immunogenic and abundant surface-exposed C. difficile cell wall protein, plays an important role in the bacterium's adherence in vitro. In this study, we aimed to analyze the homology and immunogenicity of Cwp2 and its protection efficacy as a vaccine candidate against CDI in mice.

METHODS

we conducted in silico analyses to assess the homology and immunogenicity of Cwp2, and we evaluated its potential as a vaccine candidate against CDI using a mouse model of immunization and infection.

RESULTS

Our in silico analyses predicted the immunogenic region (functional domain) of Cwp2 and revealed its high homology among various toxinotypes and ribotypes (R.T.s) or sequence types (S.T.s). Immunizations of mice with the Cwp2 functional domain (Cwp2_A) induced potent IgG/A antibody responses against Cwp2_A, protected mice from CDI, and reduced C. difficile spore and toxin levels in feces post-infection. Additionally, anti-Cwp2_A sera inhibited the binding of C. difficile vegetative cells to HCT8 cells.

CONCLUSIONS

Our report demonstrates for the first time the potential of Cwp2_A as an effective vaccine candidate against CDI in mice.

Design Principles for Immunomodulatory Biomaterials

The immune system is imperative to the survival of all biological organisms. A functional immune system protects the organism by detecting and eliminating foreign and host aberrant molecules. Conversely, a dysfunctional immune system characterized by an overactive or weakened immune system causes life-threatening autoimmune or immunodeficiency diseases. Therefore, a critical need exists to develop technologies that regulate the immune system to ensure homeostasis or treat several diseases. Accumulating evidence shows that biomaterials─artificial materials (polymers, metals, ceramics, or engineered cells and tissues) that interact with biological systems─can trigger immune responses, offering a materials science-based strategy to modulate the immune system. This Review discusses the expanding frontiers of biomaterial-based immunomodulation, focusing on principles for designing these materials. This Review also presents examples of immunomodulatory biomaterials, which include polymers and metal- and carbon-based nanomaterials, capable of regulating the innate and adaptive immune systems.

miR-351-5p regulation of CPEB3 affecting aluminium-induced learning and memory impairment in SD rats

Aluminium exposure has been found to impair learning and memory abilities; however, the underlying molecular mechanisms remain unclear. In this study we conducted a double luciferase reporter assay to determine whether miR-351-5p regulates cytoplasmic polyadenylation element binding protein (CPEB) 3 mRNA. To this end, we overexpressed and inhibited miR-351-5p via stereotaxic microinjections of adeno-associated virus (AAV) into the hippocampus of Sprague Dawley rats in a sub-chronic aluminium exposure model to examine learning and memory ability using Morris water maze. Ultrastructural electron microscopy and Golgi staining were used to examine morphological changes in hippocampal neurons. In addition, we examined the levels of synaptic plasticity-related proteins (PRPs) and CPEB3 to determine the involvement of the miR-351-5P/CPEB3/PRPs pathway in aluminium neurotoxicity. Sub-chronic aluminium exposure reduced the spatial learning and memory ability of rats. Overexpression of AAV-miR-351-5P in the hippocampus aggravated the impairment of spatial learning and memory abilities of aluminium-treated rats, whereas inhibition of AAV-miR-351-5p expression alleviated it. Western blotting suggested that sub-chronic aluminium exposure increased miR-351-5p levels and reduced the expression of CPEB3 and PRPs in the hippocampus. Treatment with an AAV-miR-351-5p inhibitor partially recovered CPEB3 and PRPs. Double luciferase reporter assay results showed that CPEB3 was a direct target of miR-351-5p, while electron microscopy suggested that aluminium could damage mitochondria and synapses in the CA1 of the hippocampus. Golgi staining results indicated that aluminium could reduce the number of dendritic spines in hippocampal neurons. Inhibition of miR-351-5p restored the synaptic structure and growth of dendritic spines in the hippocampus. The involvement of the miR-351-5P/CPEB3/RPPs pathway in aluminium neurotoxicity was confirmed. Our findings suggest that inhibition of miR-351-5p can alleviate learning and memory impairments by increasing CPEB3 and PRPs.

Immunogenicity analysis based on VP1 and VP2 proteins of bovine enterovirus

Bovine enterovirus (BEV) infection manifests as a spectrum of clinical signs affecting the respiratory, gastrointestinal, and reproductive systems in cattle. Outbreaks of this disease results in large economic losses to the bovine industry worldwide. Currently there are no efficacious vaccines and medicines to prevent BEV infection. In the present study, reverse transcription-polymerase chain reaction was used to amplify the VP1 and VP2 genes of BEV, enabling the synthesis of a chimeric recombinant protein which contained partial sequences from both proteins. Subsequently, the emulsified purified proteins with Freund's adjuvant were used for triple-fold immunization of 4-week-old Institute of Cancer Research (ICR) mice. The mice were subsequently subjected to a challenge assay which elicited an immune response that was characterized by elevated titers of BEV-specific neutralizing antibodies. Notably, the results showed that the purification of pET32a-VP1 and pET32a-VP2 proteins markedly curtailed virus excretion and mitigated the histopathological damage usually associated with BEV infections. These were observed in the small intestines, kidneys and brain in infected animals. It also alleviated clinical symptoms such as hypothermia and weight loss. In summary, this study offers a theoretical and practical basis for BEV vaccine development.

Glycoside-Mediated Enhancement of Stability in Aluminum Oxyhydroxide Nanoadjuvants during Freeze-Drying

Aluminum-based adjuvants have been indispensable to vaccine potency. However, their effectiveness is difficult to maintain after freeze-drying, which limits the storage and application of aluminum-adjuvanted vaccines. In this study, the impact of freeze-drying on aluminum oxyhydroxide nanorods (AlOOH NRs) was investigated. Freeze-drying led to aggregation and resulted in the loss of the surface hydroxyl content of aluminum adjuvants. To alleviate freeze-drying-induced damage, the potency of different alkyl glycosides as protectants was further evaluated. It was demonstrated that the structural balance of the head and tail of a glycoside was more conducive to protecting AlOOH NRs from aggregation and loss of surface hydroxyl groups. These results underline the proper selection of protectants to protect adjuvants against functional defects caused by freeze-drying, which is important for the stability and efficacy of vaccines and biopharmaceutical products.

Immune Responses to Respiratory Syncytial Virus Vaccines: Advances and Challenges

Respiratory Syncytial Virus (RSV) is a leading cause of acute respiratory infections, particularly in children and the elderly. This virus primarily infects ciliated epithelial cells and activates alveolar macrophages and dendritic cells, triggering an innate antiviral response that releases pro-inflammatory cytokines. However, immunity generated by infection is limited, often leading to reinfection throughout life. This review focuses on the immune response elicited by newly developed and approved vaccines against RSV. A comprehensive search of clinical studies on RSV vaccine candidates conducted between 2013 and 2024 was performed. There are three primary target groups for RSV vaccines: pediatric populations, infants through maternal immunization, and the elderly. Different vaccine approaches address these groups, including subunit, live attenuated or chimeric, vector-based, and mRNA vaccines. To date, subunit RSV vaccines and the mRNA vaccine have been approved using the pre-fusion conformation of the F protein, which has been shown to induce strong immune responses. Nevertheless, several other vaccine candidates face challenges, such as modest increases in antibody production, highlighting the need for further research. Despite the success of the approved vaccines for adults older than 60 years and pregnant women, there remains a critical need for vaccines that can protect children older than six months, who are still highly vulnerable to RSV infections.

Next-generation aluminum adjuvants: Immunomodulatory layered double hydroxide NanoAlum reengineered from first-line drugs

Aluminum adjuvants (Alum), approved by the US Food and Drug Administration, have been extensively used in vaccines containing recombinant antigens, subunits of pathogens, or toxins for almost a century. While Alums typically elicit strong humoral immune responses, their ability to induce cellular and mucosal immunity is limited. As an alternative, layered double hydroxide (LDH), a widely used antacid, has emerged as a novel class of potent nano-aluminum adjuvants (NanoAlum), demonstrating advantageous physicochemical properties, biocompatibility and adjuvanticity in both humoral and cellular immune responses. In this review, we summarize and compare the advantages and disadvantages of Alum and NanoAlum in these properties and their performance as adjuvants. Moreover, we propose the key features for ideal adjuvants and demonstrate that LDH NanoAlum is a promising candidate by summarizing its current progress in immunotherapeutic cancer treatments. Finally, we conclude the review by offering our integrated perspectives about the remaining challenges and future directions for NanoAlum's application in preclinical/clinical settings.

Comparison of Hepatitis B Surface Antibody Levels After Vaccination With Combined One Dose of Hexavalent Vaccine and Two Doses of Pentavalent Vaccine Versus Three Doses of Pentavalent Vaccine

BACKGROUND

Vaccination can effectively prevent hepatitis B virus (HBV) infection. Vaccination with 3 doses of hexavalent HBV-containing vaccines led to a higher Hepatitis B surface antibody (anti-HBs) antibody level than vaccination with 3 doses of pentavalent HBV-containing vaccines. Whether the substitution of one dose of hexavalent HBV-containing vaccine in the pentavalent regimen could lead to a higher anti-HBs antibody level remains unknown.

METHODS

A randomized, open-label controlled trial was conducted. Infants 30-120 days of age were randomly assigned to either a combined hexavalent/pentavalent regimen (hexavalent HBV-containing vaccine at 2 months of age and pentavalent HBV-containing vaccine at 4 and 6 months of age) or a 3-dose pentavalent regimen (pentavalent HBV-containing vaccine at 2, 4, and 6 months of age). Anti-HBs antibody levels were measured 3-6 months after the last vaccination.

RESULTS

Seventy-six infants were enrolled, 38 in each group. The geometric mean of anti-HBs antibody levels in the combined hexavalent/pentavalent group was significantly higher than that of the 3-dose pentavalent group [316.2 mIU/mL (95% CI: 173.8-575.4 mIU/mL) versus 81.3 mIU/mL (95% CI: 38.9-169.8 mIU/mL), P = 0.006]. By multivariate analysis, the combined hexavalent/pentavalent regimen (coefficient 0.57; P = 0.003) was associated with higher anti-HBs antibody levels, while body weight <10th percentile (coefficient -0.85; P = 0.006) and receiving concomitant pneumococcal conjugated vaccines (coefficient -0.65; P = 0.001) were associated with lower anti-HBs antibody levels.

CONCLUSION

Substituting the first dose with a hexavalent HBV-containing vaccine in the pentavalent regimen for HBV vaccination led to higher anti-HBs antibody levels in infants. Concomitant pneumococcal conjugated vaccine administration may have an adverse impact on anti-HBs antibody level.

Basic Properties and Development Status of Aluminum Adjuvants Used for Vaccines

BACKGROUND

Aluminum adjuvants, renowned for their safety and efficacy, act as excellent adsorbents and vaccine immunogen enhancers, significantly contributing to innate, endogenous, and humoral immunity. An ideal adjuvant not only boosts the immune response but also ensures optimal protective immunity. Aluminum adjuvants are the most widely used vaccine adjuvants and have played a crucial role in both the prevention of existing diseases and the development of new vaccines. With the increasing emergence of new vaccines, traditional immune adjuvants are continually being researched and upgraded. The future of vaccine development lies in the exploration and integration of novel adjuvant technologies that surpass the capabilities of traditional aluminum adjuvants. One promising direction is the incorporation of nanoparticles, which offer precise delivery and controlled release of antigens, thereby enhancing the overall immune response.

CONCLUSIONS

This review summarizes the types, mechanisms, manufacturers, patents, advantages, disadvantages, and future prospects of aluminum adjuvants. Although aluminum adjuvants have certain limitations, their contribution to enhancing vaccine immunity is significant and cannot be ignored. Future research should continue to explore their mechanisms of action and address potential adverse reactions to achieve improved vaccine efficacy.

ASIA Syndrome: State-of-the-Art and Future Perspectives

The expression "Autoimmune/inflammatory syndrome induced by adjuvants (ASIA)" was coined by Shoenfeld and colleagues in 2011. It defines a group of immune-mediated disorders that arise in people, with a genetic predisposition, following exposure to adjuvant agents. This syndrome has been reported after contact with silicone implants, medications, infections, metals, vaccines, and other substances. It typically occurs in individuals with a genetic predisposition, particularly involving genes, such as HLA-DRB1 (major histocompatibility complex, class II, DR beta 1) and PTPN22 (protein tyrosine phosphatase non-receptor type 22). Some stimuli lead to an overactivation of the immune system, prompt the production of autoantibodies, and finally cause autoimmune disorders. This narrative review aims to provide an overview of the ASIA syndrome with a special focus on the role of adjuvants in different vaccines, especially after the COVID-19 pandemic, and insights into development of new treatments.

Revisiting the dimensions of universal vaccine with special focus on COVID-19: Efficacy versus methods of designing

Even though the use of SARS-CoV-2 vaccines during the COVID-19 pandemic showed unprecedented success in a short time, it also exposed a flaw in the current vaccine design strategy to offer broad protection against emerging variants of concern. However, developing broad-spectrum vaccines is still a challenge for immunologists. The development of universal vaccines against emerging pathogens and their variants appears to be a practical solution to mitigate the economic and physical effects of the pandemic on society. Very few reports are available to explain the basic concept of universal vaccine design and development. This review provides an overview of the innate and adaptive immune responses generated against vaccination and essential insight into immune mechanisms helpful in designing universal vaccines targeting influenza viruses and coronaviruses. In addition, the characteristics, safety, and factors affecting the efficacy of universal vaccines have been discussed. Furthermore, several advancements in methods worthy of designing universal vaccines are described, including chimeric immunogens, heterologous prime-boost vaccines, reverse vaccinology, structure-based antigen design, pan-reactive antibody vaccines, conserved neutralizing epitope-based vaccines, mosaic nanoparticle-based vaccines, etc. In addition to the several advantages, significant potential constraints, such as defocusing the immune response and subdominance, are also discussed.

Transforming vaccinology

The COVID-19 pandemic placed the field of vaccinology squarely at the center of global consciousness, emphasizing the vital role of vaccines as transformative public health tools. The impact of vaccines was recently acknowledged by the award of the 2023 Nobel Prize in Physiology or Medicine to Katalin Kariko and Drew Weissman for their seminal contributions to the development of mRNA vaccines. Here, we provide a historic perspective on the key innovations that led to the development of some 27 licensed vaccines over the past two centuries and recent advances that promise to transform vaccines in the future. Technological revolutions such as reverse vaccinology, synthetic biology, and structure-based design transformed decades of vaccine failures into successful vaccines against meningococcus B and respiratory syncytial virus (RSV). Likewise, the speed and flexibility of mRNA vaccines profoundly altered vaccine development, and the advancement of novel adjuvants promises to revolutionize our ability to tune immunity. Here, we highlight exciting new advances in the field of systems immunology that are transforming our mechanistic understanding of the human immune response to vaccines and how to predict and manipulate them. Additionally, we discuss major immunological challenges such as learning how to stimulate durable protective immune response in humans.

Evaluating the possible genotoxicity of nanoaluminum incorporated in human vaccines and the potential protective role of nanocurcumin: an in vivo study

For nearly 90 years, aluminum (Al) salts have been utilized as vaccination adjuvants. Nevertheless, there is a risk of adverse effects associated with the amount of nanoaluminum used in various national pediatric immunization regimens. This study aimed to investigate the possible genotoxic effects of nanoaluminum incorporated in human vaccines on the brains of newborn albino rats and whether nanocurcumin has a potential protective effect against this toxicity. Fifty newborn albino rats were randomly assigned to 5 groups, with 10 in each group. Groups 1 and 2 received "high" and "low" Al injections corresponding to either the American or Scandinavian pediatric immunization schedules, respectively, as opposed to the control rats (group 5) that received saline injections. Groups 3 and 4 received the same regimens as groups 1 and 2 in addition to oral nanocurcumin. The expression of both the cell breakdown gene tumor protein (P53) and the cell stress gene uncoupling protein 2 (UCP2) was significantly greater in groups 1 and 2 than in group 5. Groups 1 and 2 exhibited severe DNA fragmentation, which was observed as DNA laddering. Nanocurcumin significantly reduced the expression of the P53 and UCP2 genes in groups 3 and 4, with very low or undetectable DNA laddering in both groups. Vaccination with nanoaluminum adjuvants can cause genotoxic effects, which can be mediated by the inflammatory response and oxidative stress, and nanocurcumin can protect against these toxic effects through the modulation of oxidative stress regulators and gene expression.

Generating prophylactic immunity against arboviruses in vertebrates and invertebrates

The World Health Organization recently declared a global initiative to control arboviral diseases. These are mainly caused by pathogenic flaviviruses (such as dengue, yellow fever and Zika viruses) and alphaviruses (such as chikungunya and Venezuelan equine encephalitis viruses). Vaccines represent key interventions for these viruses, with licensed human and/or veterinary vaccines being available for several members of both genera. However, a hurdle for the licensing of new vaccines is the epidemic nature of many arboviruses, which presents logistical challenges for phase III efficacy trials. Furthermore, our ability to predict or measure the post-vaccination immune responses that are sufficient for subclinical outcomes post-infection is limited. Given that arboviruses are also subject to control by the immune system of their insect vectors, several approaches are now emerging that aim to augment antiviral immunity in mosquitoes, including Wolbachia infection, transgenic mosquitoes, insect-specific viruses and paratransgenesis. In this Review, we discuss recent advances, current challenges and future prospects in exploiting both vertebrate and invertebrate immune systems for the control of flaviviral and alphaviral diseases.

Aluminum hydroxide and immunostimulatory glycolipid adjuvant combination for enhanced COVID-19 subunit vaccine immunogenicity

Protein-based subunit vaccines like RBD-Fc are promising tools to fight COVID-19. RBD-Fc fuses the receptor-binding domain (RBD) of the SARS-CoV-2 virus spike protein with the Fc region of human IgG1, making it more immunogenic than RBD alone. Earlier work showed that combining RBD-Fc with iNKT cell agonists as adjuvants improved neutralizing antibodies but did not sufficiently enhance T cell responses, a limitation RBD-Fc vaccines share with common adjuvants. Here we demonstrate that aluminum hydroxide combined with α-C-GC, a C-glycoside iNKT cell agonist, significantly improved the RBD-Fc vaccine's induction of RBD-specific T-cell responses. Additionally, aluminum hydroxide with α-GC-CPOEt, a phosphonate diester derivative, synergistically elicited more robust neutralizing antibodies. Remarkably, modifying αGC with phosphate (OPO3H2) or phosphonate (CPO3H2) to potentially enhance aluminum hydroxide interaction did not improve efficacy over unmodified αGC with aluminum hydroxide. These findings underscore the straightforward yet potent potential of this approach in advancing COVID-19 vaccine development and provide insights for iNKT cell-based immunotherapy.

Manganese-Modified Aluminum Adjuvant Enhances both Humoral and Cellular Immune Responses

Aluminum adjuvants remain the most commonly used vaccine adjuvants. Being rather effective in triggering humoral immunity, however, aluminum adjuvants usually show limited abilities in activating cellular immunities. Herein, by adding manganese ions during the preparation of aluminum adjuvant, a manganese-modified aluminum (Mn-Al) adjuvant is obtained, which can effectively stimulate both humoral and cellular immune responses. Such Mn-Al adjuvant can enhance antigen adsorption and promote antigen internalization by dendritic cells (DCs). Subsequently, the released Mn2+ can activate the cyclic guanosine monophosphate-adenosine monophosphate synthase-stimulator of interferon genes pathway to further promote DC activation. When combines with the model antigen ovalbumin (OVA), the Mn-Al-adjuvantes vaccine can induce high levels of antigen-specific antibody titers and high proportions of antigen-specific cytotoxic T cells in vivo. Moreover, the Mn-Al-adjuvanted vaccine elicited stronger antigen-specific humoral and cellular immune responses than high-dose of the aluminum-based adjuvant. Additionally, immunization of mice with OVA in the presence of the Mn-Al adjuvant significantly inhibited the growth of B16-OVA tumors. Furthermore, when formulated with human papillomavirus antigens, Mn-Al-adjuvanted vaccines show better in vivo vaccination performance than aluminum-adjuvanted vaccines. Therefore, the manganese-modified aluminum adjuvant may thus become a new vaccine adjuvant with the potential to replace conventional aluminum adjuvants.

Structure-Activity Relationship Studies in Benzothiadiazoles as Novel Vaccine Adjuvants

Extracellular vesicles (EVs) can transfer antigens and immunomodulatory molecules, and such EVs released by antigen-presenting cells equipped with immunostimulatory functions have been utilized for vaccine formulations. A prior high-throughput screening campaign led to the identification of compound 634 (1), which enhanced EV release and increased intracellular Ca2+ influx. Here, we performed systematic structure-activity relationship (SAR) studies to investigate the scaffold for its potency as a vaccine adjuvant. Synthesized compounds were analyzed in vitro for CD63 reporter activity (a marker for EV biogenesis) in human THP-1 cells, induction of Ca2+ influx, IL-12 production, and cell viability in murine bone-marrow-derived dendritic cells. The SAR studies indicated that the ester functional group was requisite, and the sulfur atom of the benzothiadiazole ring replaced with a higher selenium atom (9f) or a bioisosteric ethenyl group (9h) retained potency. Proof-of-concept vaccination studies validated the potency of the selected compounds as novel vaccine adjuvants.

Toxicity and biokinetics following pulmonary exposure to aluminium (aluminum): A review

During the manufacture and use of aluminium (aluminum), inhalation exposure may occur. We reviewed the pulmonary toxicity of this metal including its toxicokinetics. The normal serum/plasma level based on 17 studies was 5.7 ± 7.7 µg Al/L (mean ± SD). The normal urine level based on 15 studies was 7.7 ± 5.3 µg/L. Bodily fluid and tissue levels during occupational exposure are also provided, and the urine level was increased in aluminium welders (43 ± 33 µg/L) based on 7 studies. Some studies demonstrated that aluminium from occupational exposure can remain in the body for years. Excretion pathways include urine and faeces. Toxicity studies were mostly on aluminium flakes, aluminium oxide and aluminium chlorohydrate as well as on mixed exposure, e.g. in aluminium smelters. Endpoints affected by pulmonary aluminium exposure include body weight, lung function, lung fibrosis, pulmonary inflammation and neurotoxicity. In men exposed to aluminium oxide particles (3.2 µm) for two hours, lowest observed adverse effect concentration (LOAEC) was 4 mg Al2O3/m3 (= 2.1 mg Al/m3), based on increased neutrophils in sputum. With the note that a similar but not statistically significant increase was seen during control exposure. In animal studies LOAECs start at 0.3 mg Al/m3. In intratracheal instillation studies, all done with aluminium oxide and mainly nanomaterials, lowest observed adverse effect levels (LOAELs) started at 1.3 mg Al/kg body weight (bw) (except one study with a LOAEL of ∼0.1 mg Al/kg bw). The collected data provide information regarding hazard identification and characterisation of pulmonary exposure to aluminium.

Water-Soluble and Freezable Aluminum Salt Vaccine Adjuvant

Particulate aluminum salts have long occupied a central place worldwide as inexpensive immunostimulatory adjuvants that enable induction of protective immunity for vaccines. Despite their huge benefits and safety, the particulate structures of aluminum salts require transportation and storage at temperatures between 2 °C and 8 °C, and they all have exquisite sensitivity to damage caused by freezing. Here, we propose to solve the critical freezing vulnerability of particulate aluminum salt adjuvants by introducing soluble aluminum salts as adjuvants. The solubility properties of fresh and frozen aluminum chloride and aluminum triacetate, each buffered optimally with sodium acetate, were demonstrated with visual observations and with UV-vis scattering analyses. Two proteins, A244 gp120 and CRM197, adjuvanted either with soluble aluminum chloride or soluble aluminum triacetate, each buffered by sodium acetate at pH 6.5-7.4, elicited murine immune responses that were equivalent to those obtained with Alhydrogel®, a commercial particulate aluminum hydroxide adjuvant. The discovery of the adjuvanticity of soluble aluminum salts might require the creation of a new adjuvant mechanism for aluminum salts in general. However, soluble aluminum salts might provide a practical substitute for particulate aluminum salts as vaccine adjuvants, thereby avoiding the risk of inactivation of vaccines due to accidental freezing of aluminum salt particles.

In vivo quantitative characterization of nano adjuvant transport in the tracheal layer by photoacoustic imaging

Adjuvants are indispensable ingredients in vaccine formulations. Evaluating the in vivo transport processes of adjuvants, particularly for inhalation formulations, presents substantial challenges. In this study, a nanosized adjuvant aluminum hydroxide (AlOOH) was synthesized and labeled with indocyanine green (ICG) and bovine serum albumin (BSA) to achieve strong optical absorption ability and high biocompatibility. The adjuvant nanomaterials (BSA@ICG@AlOOH, BIA) were delivered as an aerosol into the airways of mice, its distribution was monitored using photoacoustic imaging (PAI) in vivo. PAI results illustrated the gradual cross-layer transmission process of BIA in the tracheal layer, traversing approximately 250 µm from the inner layer of the trachea to the outer layer. The results were consistent with pathology. While the intensity of the BIA reduced by approximately 46.8% throughout the transport process. The ability of PAI for quantitatively characterized the dynamic transport process of adjuvant within the tracheal layer may be widely used in new vaccine development.

A TLR4 ligand-based adjuvant for promoting the immunogenicity of typhoid subunit vaccines

None of the typhoid Vi Polysaccharide (ViPS) subunit vaccines incorporate adjuvants, and the immunogenicity of ViPS vaccines (e.g. Typbar TCV® and Typhim Vi®) is in part due to associated TLR4 ligands such as endotoxin present in these vaccines. Since endotoxin content in vaccines is variable and kept very low due to inherent toxicity, it was hypothesized that incorporating a defined amount of a non-toxic TLR4-ligand such as monophosphoryl lipid A in ViPS vaccines would improve their immunogenicity. To test this hypothesis, a monophosphoryl lipid A-based adjuvant formulation named Turbo was developed. Admixing Turbo with Typbar TCV® (ViPS-conjugated to tetanus toxoid) increased the levels of anti-ViPS IgM, IgG1, IgG2b, IgG2a/c, and IgG3 in inbred and outbred mice. In infant mice, a single immunization with Turbo adjuvanted Typbar TCV® resulted in a significantly increased and durable IgG response and improved the control of bacterial burden compared to mice immunized without Turbo. Similarly, when adjuvanted with Turbo, the antibody response and control of bacteremia were also improved in mice immunized with Typhim Vi®, an unconjugated vaccine. The immunogenicity of unconjugated ViPS is inefficient in young mice and is lost in adult mice when immunostimulatory ligands in ViPS are removed. Nevertheless, when adjuvanted with Turbo, poorly immunogenic ViPS induced a robust IgG response in young and adult mice, and this was observed even under antigen-limiting conditions. These data suggest that incorporation of Turbo as an adjuvant will make typhoid vaccines more immunogenic regardless of their intrinsic immunogenicity or conjugation status and maximize the efficacy across all ages.

Vaccine adjuvants: Tailoring innate recognition to send the right message

Adjuvants play pivotal roles in vaccine development, enhancing immunization efficacy through prolonged retention and sustained release of antigen, lymph node targeting, and regulation of dendritic cell activation. Adjuvant-induced activation of innate immunity is achieved via diverse mechanisms: for example, adjuvants can serve as direct ligands for pathogen recognition receptors or as inducers of cell stress and death, leading to the release of immunostimulatory-damage-associated molecular patterns. Adjuvant systems increasingly stimulate multiple innate pathways to induce greater potency. Increased understanding of the principles dictating adjuvant-induced innate immunity will subsequently lead to programming specific types of adaptive immune responses. This tailored optimization is fundamental to next-generation vaccines capable of inducing robust and sustained adaptive immune memory across different cohorts.

Improving Bioprocess Conditions for the Production of Prodigiosin Using a Marine Serratia rubidaea Strain

The enormous potential attributed to prodigiosin regarding its applicability as a natural pigment and pharmaceutical agent justifies the development of sound bioprocesses for its production. Using a Serratia rubidaea strain isolated from a shallow-water hydrothermal vent, optimization of the growth medium composition was carried out. After medium development, the bacterium temperature, light and oxygen needs were studied, as was growth inhibition by product concentration. The implemented changes led to a 13-fold increase in prodigiosin production in a shake flask, reaching 19.7 mg/L. The conditions allowing the highest bacterial cell growth and prodigiosin production were also tested with another marine strain: S. marcescens isolated from a tide rock pool was able to produce 15.8 mg/L of prodigiosin. The bioprocess with S. rubidaea was scaled up from 0.1 L shake flasks to 2 L bioreactors using the maintenance of the oxygen mass transfer coefficient (kLa) as the scale-up criterion. The implemented parameters in the bioreactor led to an 8-fold increase in product per biomass yield and to a final concentration of 293.1 mg/L of prodigiosin in 24 h.

Th2 and Th17-associated immunopathology following SARS-CoV-2 breakthrough infection in Spike-vaccinated ACE2-humanized mice

Vaccines have demonstrated remarkable effectiveness in protecting against COVID-19; however, concerns regarding vaccine-associated enhanced respiratory diseases (VAERD) following breakthrough infections have emerged. Spike protein subunit vaccines for SARS-CoV-2 induce VAERD in hamsters, where aluminum adjuvants promote a Th2-biased immune response, leading to increased type 2 pulmonary inflammation in animals with breakthrough infections. To gain a deeper understanding of the potential risks and the underlying mechanisms of VAERD, we immunized ACE2-humanized mice with SARS-CoV-2 Spike protein adjuvanted with aluminum and CpG-ODN. Subsequently, we exposed them to increasing doses of SARS-CoV-2 to establish a breakthrough infection. The vaccine elicited robust neutralizing antibody responses, reduced viral titers, and enhanced host survival. However, following a breakthrough infection, vaccinated animals exhibited severe pulmonary immunopathology, characterized by a significant perivascular infiltration of eosinophils and CD4+ T cells, along with increased expression of Th2/Th17 cytokines. Intracellular flow cytometric analysis revealed a systemic Th17 inflammatory response, particularly pronounced in the lungs. Our data demonstrate that aluminum/CpG adjuvants induce strong antibody and Th1-associated immunity against COVID-19 but also prime a robust Th2/Th17 inflammatory response, which may contribute to the rapid onset of T cell-mediated pulmonary immunopathology following a breakthrough infection. These findings underscore the necessity for further research to unravel the complexities of VAERD in COVID-19 and to enhance vaccine formulations for broad protection and maximum safety.

Enhancing Inactivated Yellow Fever 17D Vaccine-Induced Immune Responses in Balb/C Mice Using Alum/CpG

There are some concerns about the safety of live attenuated yellow fever vaccines (YF-live), particularly viscerotropic adverse events, which have a high mortality rate. The cellular production of the vaccine will not cause these adverse effects and has the potential to extend applicability to those who have allergic reactions, immunosuppression, and age. In this study, inactivated yellow fever (YF) was prepared and adsorbed with Alum/CpG. The cellular and humoral immunities were investigated in a mouse model. The results showed that Alum/CpG (20 μg/mL) could significantly increase the binding and neutralizing activities of the antibodies against YF. Moreover, the antibody level at day 28 after one dose was similar to that of the attenuated vaccine, but significantly higher after two doses. At the same time, Alum/CpG significantly increased the levels of IFN-γ and IL-4 cytokines.