Towards an understanding of the adjuvant action of aluminium

Exploring the Papillomaviral Proteome to Identify Potential Candidates for a Chimeric Vaccine against Cervix Papilloma Using Immunomics and Computational Structural Vaccinology

The human papillomavirus (HPV) 58 is considered to be the second most predominant genotype in cervical cancer incidents in China. HPV type-restriction, non-targeted delivery, and the highcost of existing vaccines necessitate continuing research on the HPV vaccine. We aimed to explore the papillomaviral proteome in order to identify potential candidates for a chimeric vaccine against cervix papilloma using computational immunology and structural vaccinology approaches. Two overlapped epitope segments (23⁻36) and (29⁻42) from the N-terminal region of the HPV58 minor capsid protein L2 are selected as capable of inducing both cellular and humoral immunity. In total, 318 amino acid lengths of the vaccine construct SGD58 contain adjuvants (Flagellin and RS09), two Th epitopes, and linkers. SGD58 is a stable protein that is soluble, antigenic, and non-allergenic. Homology modeling and the structural refinement of the best models of SGD58 and TLR5 found 96.8% and 93.9% favored regions in Rampage, respectively. The docking results demonstrated a HADDOCK score of -62.5 ± 7.6, the binding energy (-30 kcal/mol) and 44 interacting amino acid residues between SGD58-TLR5 complex. The docked complex are stable in 100 ns of simulation. The coding sequences of SGD58 also show elevated gene expression in Escherichia coli with 1.0 codon adaptation index and 59.92% glycine-cysteine content. We conclude that SGD58 may prompt the creation a vaccine against cervix papilloma.

Reprogramming the adjuvant properties of aluminum oxyhydroxide with nanoparticle technology

Aluminum salts, developed almost a century ago, remain the most commonly used adjuvant for licensed human vaccines. Compared to more recently developed vaccine adjuvants, aluminum adjuvants such as Alhydrogel are heterogeneous in nature, consisting of 1–10 micrometer-sized aggregates of nanoparticle aluminum oxyhydroxide fibers. To determine whether the particle size and aggregated state of aluminum oxyhydroxide affects its adjuvant activity, we developed a scalable, top-down process to produce stable nanoparticles (nanoalum) from the clinical adjuvant Alhydrogel by including poly(acrylic acid) (PAA) polymer as a stabilizing agent. Surprisingly, the PAA:nanoalum adjuvant elicited a robust TH1 immune response characterized by antigen-specific CD4⁺ T cells expressing IFN-γ and TNF, as well as high IgG2 titers, whereas the parent Alhydrogel and PAA elicited modest TH2 immunity characterized by IgG1 antibodies. ASC, NLRP3 and the IL-18R were all essential for TH1 induction, indicating an essential role of the inflammasome in this adjuvant’s activity. Compared to microparticle Alhydrogel this nanoalum adjuvant provided superior immunogenicity and increased protective efficacy against lethal influenza challenge. Therefore PAA:nanoalum represents a new class of alum adjuvant that preferentially enhances TH1 immunity to vaccine antigens. This adjuvant may be widely beneficial to vaccines for which TH1 immunity is important, including tuberculosis, pertussis, and malaria.

Aluminum salt-based adjuvants such as alhydrogel have been a mainstay of vaccines for decades. Christopher B. Fox and colleagues at the Infectious Disease Research Institute in Seattle, USA, investigate the effect adjuvant particle size has on experimental vaccine responses. Shearing conventional micrometer-scale alhyrodogel into nanoparticles is followed by rapid reaggregation; however, the authors show that addition of anionic polymer (PAA) prevents this and results in stable nanoparticles (PAA:nanoalum). Used as an adjuvant with either influenza or TB antigens triggers robust TH1 and IgG2a responses that are superior to alhydrogel even when the latter includes a Toll-like receptor 4 (TLR4) agonist. Interestingly, addition of TLR4 agonist to PAA:nanoalum actually impairs its adjuvanticity. PAA:nanoalum efficacy is nevertheless dependent on the NLRP3 inflammasome suggesting that this novel adjuvant somehow triggers this pathway through some as yet undefined route.

Uniform dendrimer-like mesoporous silica nanoparticles as a nano-adjuvant for foot-and-mouth disease virus-like particle vaccine

Dendrimer-like mesoporous silica nanoparticles (MSNs) with large center-radial mesopores have been prepared for macromolecular protein loading and delivery.

Alum-functionalized graphene oxide nanocomplexes for effective anticancer vaccination

Aluminum-based adjuvant (e.g., aluminum oxyhydroxide (AlO(OH), known as the commercial Alhydrogel® (Alum)) is the first adjuvant to be used in human vaccines. Although Alum shows a robust induction of antibody-mediated immunity, its weak stimulation of cell-mediated immunity makes it a questionable adjuvant for cancer immunotherapy. Herein, we described a novel formulation of Alum-based adjuvant by preparing AlO(OH)-modified graphene oxide (GO) nanosheets (GO-AlO(OH)), which, in addition to maintaining the induction of humoral immune response by AlO(OH), could further elicit the cellular immune response by GO. Similar to Alum, GO-AlO(OH) vaccine formulation could be constructed by the incorporation of antigen using a facile mixing/adsorption approach. Antigen-loaded GO-AlO(OH) nanocomplexes facilitated cellular uptake and cytosolic release of antigens and promoted DC maturation, thereby eliciting higher antigen-specific IgG titers, inducing robust CD4⁺ and CD8⁺ T lymphocyte response, and inhibiting tumor growth in vivo. Furthermore, by employing tumor cell lysate-based cancer vaccines, GO-AlO(OH) nanocomplexes led to significant inhibition of tumor growth and can be implemented as a personalized treatment strategy for cancer vaccine development. Overall, GO-AlO(OH) nanocomplexes described herein may serve as a facile and efficient approach for effective anticancer vaccination. STATEMENT OF SIGNIFICANCE: Herein, we described a novel formulation of aluminum-based adjuvant by preparing aluminum oxyhydroxide (AlO(OH)) (known as "Alum")-modified graphene oxide (GO) nanocomplexes (GO-AlO(OH)), which, in addition to maintaining the induction of humoral immune response by AlO(OH), could further elicit the cellular immune response by GO. GO-AlO(OH) nanocomplexes can be prepared easily and in large scale by a chemical precipitation method. Similar to "Alum," antigen-loaded GO-AlO(OH) vaccine formulation could be constructed by the incorporation of antigen using a facile mixing/adsorption approach. The very simple and reproductive preparation process of vaccines and the powerful ability to raise both humoral and cellular immune responses provide a novel approach for improving cancer immunotherapy efficacy.

A supramolecular hydrogel to boost the production of antibodies for phosphorylated proteins

We reported on a method of using hydrogels to selectively increase the production of antibodies for phosphorylated proteins.

Self-healing encapsulation and controlled release of vaccine antigens from PLGA microparticles delivered by microneedle patches

There is an urgent need to reduce reliance on hypodermic injections for many vaccines to increase vaccination safety and coverage. Alternative approaches include controlled release formulations, which reduce dosing frequencies, and utilizing alternative delivery devices such as microneedle patches (MNPs). This work explores development of controlled release microparticles made of poly (lactic-co-glycolic acid) (PLGA) that stably encapsulate various antigens though aqueous active self-healing encapsulation (ASE). These microparticles are incorporated into rapid-dissolving MNPs for intradermal vaccination. PLGA microparticles containing Alhydrogel are loaded with antigens separate from microparticle fabrication using ASE. This avoids antigen expsoure to many stressors. The microparticles demonstrate bi-phasic release, with initial burst of soluble antigen, followed by delayed release of Alhydrogel-complexed antigen over approximately 2 months in vitro. For delivery, the microparticles are incorporated into MNPs designed with pedestals to extend functional microneedle length. These microneedles readily penetrate skin and rapidly dissolve to deposit microparticles intradermally. Microparticles remain in the tissue for extended residence, with MNP-induced micropores resealing readily. In animal models, these patches generate robust immune responses that are comparable to conventional administration techniques. This lays the framework for a versatile vaccine delivery system that could be self-applied with important logistical advantages over hypodermic injections.

Trained Innate Immunity and Its Implications for Mucosal Immunity and Inflammation

The long-standing dogma that immunological memory is the exclusive prerogative of the adaptive immune system has been challenged by emerging evidence that innate immunity can also maintain memory of past events. Such immunological imprinting takes two forms, trained innate immunity and tolerance. Trained immunity involves metabolic and epigenetic adaptations in innate immune cells and their progenitors in the bone marrow upon exposure to certain microbial and/or inflammatory stimuli so that the "trained" cells would be poised to respond much faster and stronger to a subsequent challenge (e.g., a new infection that is not necessarily the same as the earlier one). Conversely, tolerance leads to attenuated immune responses to secondary stimuli. This review focuses on trained immunity and discusses evidence for its existence from lower organisms to humans, its mechanistic underpinnings, and its translational ramifications. Although trained immunity can be considered as an evolutionarily conserved beneficial response against reinfections, in the setting of modern societies with high prevalence of chronic mucosal and systemic inflammatory diseases, trained immunity could also promote maladaptive immune responses that aggravate pathology. Thus, depending on context, innate immune memory could be therapeutically manipulated using defined agonists to either promote innate immune responses (particularly useful for the treatment of infections or chemotherapy-induced myelosuppression) or suppress excessive inflammation in inflammatory and autoimmune diseases.

Introduction to the Immune System

The immune system in a broad sense is a mechanism that allows a living organism to discriminate between "self" and "nonself." Examples of immune systems occur in multicellular organisms as simple and ancient as sea sponges. In fact, complex multicellular life would be impossible without the ability to exclude external life from the internal environment. This introduction to the immune system will explore the cell types and soluble factors involved in immune reactions, as well as their location in the body during development and maintenance. Additionally, a description of the immunological events during an innate and adaptive immune reaction to an infection will be discussed, as well as a brief introduction to autoimmunity, cancer immunity, vaccines, and immunotherapies.

Sulfated archaeol glycolipids: Comparison with other immunological adjuvants in mice

Archaeosomes are liposomes traditionally comprised of total polar lipids (TPL) or semi-synthetic glycerolipids of ether-linked isoprenoid phytanyl cores with varied glyco- and amino-head groups. As adjuvants, they induce robust, long-lasting humoral and cell-mediated immune responses and enhance protection in murine models of infectious disease and cancer. Traditional total polar lipid (TPL) archaeosome formulations are relatively complex and first generation semi-synthetic archaeosomes involve many synthetic steps to arrive at the final desired glycolipid composition. We have developed a novel archaeosome formulation comprising a sulfated disaccharide group covalently linked to the free sn-1 hydroxyl backbone of an archaeal core lipid (sulfated S-lactosylarchaeol, SLA) that can be more readily synthesized yet retains strong immunostimulatory activity for induction of cell-mediated immunity following systemic immunization. Herein, we have evaluated the immunostimulatory effects of SLA archaeosomes when used as adjuvant with ovalbumin (OVA) and hepatitis B surface antigen (HBsAg) and compared this to various other adjuvants including TLR3/4/9 agonists, oil-in-water and water-in-oil emulsions and aluminum hydroxide. Overall, we found that semi-synthetic sulfated glycolipid archaeosomes induce strong Ag-specific IgG titers and CD8 T cells to both antigens. In addition, they induce the expression of a number of cytokines/chemokines including IL-6, G-CSF, KC & MIP-2. SLA archaeosome formulations demonstrated strong adjuvant activity, superior to many of the other tested adjuvants.

Adjuvant activity of ethanol extract of Hippophae rhamnoides leaves with inactivated rabies virus antigen

CONTEXT

Hippophae rhamnoides L. (Elaeagnaceae), commonly known as seabuckthorn (SBT), is known for its medicinal and nutritional properties.

OBJECTIVE

Evaluation of in vivo adjuvant activity of SBT leaf extract (SBTE) with inactivated rabies virus antigen (Rb).

MATERIALS AND METHODS

Swiss albino mice were immunized with aqueous-alcoholic SBTE (100 mg/kg body weight) or algel (aluminium hydroxide gel) with or without Rb (5% v/v). After priming, booster was administered on day 14. Rabies virus neutralizing antibody (RVNA) titers were estimated by rapid fluorescent focus inhibition test in sera samples collected on days 7, 14, 21, 28 and 35. Effect of adjuvant administration on cytotoxic T lymphocytes (CTLs), memory T cells, plasma and CD11c⁺ cells was studied by flow cytometry. In vitro hemolysis was assayed in human RBC.

RESULTS

RVNA titers were significantly enhanced (p < 0.05) after booster administration in mice immunized with SBTE + Rb as compared to the controls. In combination, SBTE, algel and Rb, enhanced the RVNA titers. CTLs significantly increased (p < 0.05) in SBTE + Rb immunized mice. Memory T cells and plasma cells were 27.9 and 15.9%, respectively, in SBTE + Rb immunized mice as compared to that of 20.3 and 11.3%, respectively, in Rb immunized group. SBTE + Rb enhanced peritoneal CD11c⁺ cells (25.8%) as compared to 9.4% cells in Rb immunized mice, showed 3.2-fold increment in LPS induced IL-1β. No RBC hemolysis was observed with SBTE.

CONCLUSIONS

This study demonstrates the potential adjuvant activity of SBTE with Rb by increasing RVNA titers and CTL response.

Physical activation of innate immunity by spiky particles

Microbial biochemicals have been indicated as the primary stimulators of innate immunity, the first line of the body's defence against infections. However, the influence of topological features on a microbe's surface on immune responses remains largely unknown. Here we demonstrate the ability of TiO₂ microparticles decorated with nanospikes (spiky particles) to activate and amplify the immune response in vitro and in vivo. The nanospikes exert mechanical stress on the cells, which results in potassium efflux and inflammasome activation in macrophages and dendritic cells during phagocytosis. The spiky particles augment antigen-specific humoral and cellular immune responses in the presence of monophosphoryl lipid A and elicit protective immunity against tumour growth and influenza viral infection. The study offers insights into how surface physical cues can tune the activation of innate immunity and provides a basis for engineering particles with increased immunogenicity and adjuvanticity.

A TLR4-derived non-cytotoxic, self-assembling peptide functions as a vaccine adjuvant in mice

Vaccination is devised/formulated to stimulate specific and prolonged immune responses for long-term protection against infection or disease. A vaccine component, namely adjuvant, enhances antigen recognition by the host immune system and thereby stimulates its cellular and adaptive responses. Especially synthetic Toll-like receptor (TLR) agonists having self-assembling properties are considered as good candidates for adjuvant development. Here, a human TLR4-derived 20-residue peptide (TR-433), present in the dimerization interface of the TLR4-myeloid differentiation protein-2 (MD2) complex, displayed self-assembly and adopted a nanostructure. Both in vitro studies and in vivo experiments in mice indicated that TR-433 is nontoxic. TR-433 induced pro-inflammatory responses in THP-1 monocytes and HEK293T cells that were transiently transfected with TLR4/CD14/MD2 and also in BALB/c mice. In light of the self-assembly and pro-inflammatory properties of TR-433, we immunized with a mixture of TR-433 and either ovalbumin or filarial antigen trehalose-6-phosphate phosphatase (TPP). A significant amount of IgG titers was produced, suggesting adjuvanting capability of TR-433 that was comparable with that of Freund's complete adjuvant (FCA) and appreciably higher than that of alum. We found that TR-433 preferentially activates type 1 helper T cell (T_h1) response rather than type 2 helper T cell (T_h2) response. To our knowledge, this is the first report on the identification of a short TLR4-derived peptide that possesses both self-assembling and pro-inflammatory properties and has significant efficacy as an adjuvant, capable of activating cellular responses in mice. These results indicate that TR-433 possesses significant potential for development as a new adjuvant in therapeutic application.

Hydroxypropyltrimethyl ammonium chloride chitosan activates RAW 264.7 macrophages through the MAPK and JAK-STAT signaling pathways

Hydroxypropyltrimethyl ammonium chloride chitosan (HACC) is a water-soluble derivative of chitosan. To investigate the immunostimulatory effects of HACC, quaternized chitosans with different molecular weights were prepared and their effects on RAW 264.7 macrophages were compared. The results showed that HACC promoted nitric oxide (NO) production in a molecular weight- and dose-dependent manner. Lower molecular weight HACC was more active in promoting NO production. Furthermore, flow cytometry analysis showed that HACC significantly promoted the production of interleukin-6 and tumor necrosis factor-α. These results were further demonstrated by quantitive real-time reverse transcription polymerase chain reaction and western blot analysis. Moreover, western blotting revealed that HACC induced the phosphorylation of extracellular signal-regulated kinase, c-Jun N-terminal kinase, p38, and signal transducer and activator of transcription (STAT) proteins. In conclusion, HACC activated RAW 264.7 cells through the mitogen-activated protein kinases and Janus kinase/STAT pathways.

Establishment of a novel safety assessment method for vaccine adjuvant development

Vaccines effectively prevent infectious diseases. Many types of vaccines against various pathogens that threaten humans are currently in widespread use. Recently, adjuvant adaptation has been attempted to activate innate immunity to enhance the effectiveness of vaccines. The effectiveness of adjuvants for vaccinations has been demonstrated in many animal models and clinical trials. Although a highly potent adjuvant tends to have high effectiveness, it also has the potential to increase the risk of side effects such as pain, edema, and fever. Indeed, highly effective adjuvants, such as poly(I:C), have not been clinically applied due to their high risks of toxicity in humans. Therefore, the task in the field of adjuvant development is to clinically apply highly effective and non- or low-toxic adjuvant-containing vaccines. To resolve this issue, it is essential to ensure a low risk of side effects and the high efficacy of an adjuvant in the early developmental phases. This review summarizes the theory and history of the current safety assessment methods for adjuvants, using the inactivated influenza vaccine as a model. Our novel method was developed as a system to judge the safety of a candidate compound using biomarkers identified by genomic technology and statistical tools. A systematic safety assessment tool for adjuvants would be of great use for predicting toxicity during novel adjuvant development, screening, and quality control.

Impact of eosinophil-peroxidase (EPX) deficiency on eosinophil structure and function in mouse airways

Eosinophil peroxidase (EPX) is a major constituent of the large cytoplasmic granules of both human and mouse eosinophilic leukocytes. Human EPX deficiency is a rare, autosomal-recessive disorder limited to the eosinophil lineage. Our intent was to explore the impact of EPX gene deletion on eosinophil content, structure, and function. In response to repetitive intranasal challenge with a filtrate of the allergen, Alternaria alternata, we found significantly fewer eosinophils peripherally and in the respiratory tracts of EPX^-/- mice compared to wild-type controls; furthermore, both the major population (Gr1^-/lo ) and the smaller population of Gr1^hi eosinophils from EPX^-/- mice displayed lower median fluorescence intensities (MFIs) for Siglec F. Quantitative evaluation of transmission electron micrographs of lung eosinophils confirmed the relative reduction in granule outer matrix volume in cells from the EPX^-/- mice, a finding analogous to that observed in human EPX deficiency. Despite the reduced size of the granule matrix, the cytokine content of eosinophils isolated from allergen-challenged EPX^{-/ -} and wild-type mice were largely comparable to one another, although the EPX^-/- eosinophils contained reduced concentrations of IL-3. Other distinguishing features of lung eosinophils from allergen-challenged EPX^-/- mice included a reduced fraction of surface TLR4⁺ cells and reduced MFI for NOD1. Interestingly, the EPX gene deletion had no impact on eosinophil-mediated clearance of gram-negative Haemophilus influenzae from the airways. As such, although no clinical findings have been associated with human EPX deficiency, our findings suggest that further evaluation for alterations in eosinophil structure and function may be warranted.

The Mevalonate Pathway Is a Druggable Target for Vaccine Adjuvant Discovery

Motivated by the clinical observation that interruption of the mevalonate pathway stimulates immune responses, we hypothesized that this pathway may function as a druggable target for vaccine adjuvant discovery. We found that lipophilic statin drugs and rationally designed bisphosphonates that target three distinct enzymes in the mevalonate pathway have potent adjuvant activities in mice and cynomolgus monkeys. These inhibitors function independently of conventional "danger sensing." Instead, they inhibit the geranylgeranylation of small GTPases, including Rab5 in antigen-presenting cells, resulting in arrested endosomal maturation, prolonged antigen retention, enhanced antigen presentation, and T cell activation. Additionally, inhibiting the mevalonate pathway enhances antigen-specific anti-tumor immunity, inducing both Th1 and cytolytic T cell responses. As demonstrated in multiple mouse cancer models, the mevalonate pathway inhibitors are robust for cancer vaccinations and synergize with anti-PD-1 antibodies. Our research thus defines the mevalonate pathway as a druggable target for vaccine adjuvants and cancer immunotherapies.

Cancer Vaccine Immunotherapy with RNA-Loaded Liposomes

Cancer vaccines may be harnessed to incite immunity against poorly immunogenic tumors, however they have failed in therapeutic settings. Poor antigenicity coupled with systemic and intratumoral immune suppression have been significant drawbacks. RNA encoding for tumor associated or specific epitopes can serve as a more immunogenic and expeditious trigger of anti-tumor immunity. RNA stimulates innate immunity through toll like receptor stimulation producing type I interferon, and it mediates potent adaptive responses. Since RNA is inherently unstable, delivery systems have been developed to protect and deliver it to intended targets in vivo. In this review, we discuss liposomes as RNA delivery vehicles and their role as cancer vaccines.

Mechanistic study of the adjuvant effect of chitosan-aluminum nanoparticles

The use of tailored particle-based adjuvants constitutes a promising way to enhance antigen-specific humoral and cellular immune responses. However, a thorough understanding of the mechanisms underlying their adjuvanticity is crucial to generate more effective vaccines. We studied the ability of chitosan-aluminum nanoparticles (CH-Al NPs), which combine the immunostimulatory effects of chitosan and aluminum salts, to promote dendritic cell activation, assess their impact on innate and adaptive immune responses, and compare the results to those reported for conventional chitosan particles (CH-Na NPs). All tested CH-NP formulations were capable of modulating cytokine secretion by dendritic cells. CH-Al NPs promoted NLRP3 inflammasome activation, enhancing the release of IL-1β without significantly inhibiting Th1 and Th17 cell-polarizing cytokines, IL-12p70 or IL-23, and induced DC maturation, but did not promote pro-inflammatory cytokine production on their own. In vivo results showed that mice injected with CH-Al NPs generated a local inflammatory response comparable to that elicited by the vaccine adjuvant alum. Importantly, after subcutaneous immunization with CH-Al NPs combined with the hepatitis B surface antigen (HBsAg), mice developed antigen-specific IgG titers in serum, nasal and vaginal washes. Overall, our results established CH-Al NPs as a potential adjuvant to enhance both innate and adaptive immune responses.

Crumpled Aluminum Hydroxide Nanostructures as a Microenvironment Dysregulation Agent for Cancer Treatment

Owing to their unique physicochemical properties, nanomaterials have become a focus of multidisciplinary research efforts including investigations of their interactions with tumor cells and stromal compartment of tumor microenvironment (TME) toward the development of next-generation anticancer therapies. Here, we report that agglomerates of radially assembled Al hydroxide crumpled nanosheets exhibit anticancer activity due to their selective adsorption properties and positive charge. This effect was demonstrated in vitro by decreased proliferation and viability of tumor cells, and further confirmed in two murine cancer models. Moreover, Al hydroxide nanosheets almost completely inhibited the growth of murine melanoma in vivo in combination with a minimally effective dose of doxorubicin. Our direct molecular dynamics simulation demonstrated that Al hydroxide nanosheets can cause significant ion imbalance in the living cell perimembranous space through the selective adsorption of extracellular anionic species. This approach to TME dysregulation could lay the foundation for development of novel anticancer therapy strategies.

Oral vaccine based on a surface immunogenic protein mixed with alum promotes a decrease in Streptococcus agalactiae vaginal colonization in a mouse model

The Surface Immunogenic Protein (SIP) of Group B Streptococcus (GBS) had been described as a good target for vaccine development. To date, SIP has been reported as a highly conserved protein, and in a mouse model it induces protection against lethal GBS challenge. Also, similar effects have been described by intranasal immunization with a SIP-based vaccine. In this study, we show the immune response induced by an oral SIP-based vaccine formulated on alum in a mouse model. Our vaccine can reduce vaginal GBS colonization and induce specific SIP-antibodies with opsonophagocytosis activities against GBS. Moreover, we observed the activation of T-cells producing IFN-γ, TNF-α, IL-10, IL-2, and increased expression of the transcription factor T-bet, suggesting a Th1-type humoral response. The oral SIP-based vaccine is a novel alternative in the development of a vaccine against GBS.

Development of a hollow mesoporous silica nanoparticles vaccine to protect against house dust mite induced allergic inflammation

Allergen specific immunotherapy (SIT) is the only specific therapeutic way for house dust mite (HDM) allergy. To improve the efficacy of SIT, hollow mesoporous silica nanoparticles (HMSNs) were used as vehicles for HDM allergen. The HMSNs were prepared and characterized. The major HDM allergen (Der f2) was loaded onto HMSNs, and the drug loading capacity and release profile were determined. Then the Der f2 loaded HMSNs were injected subcutaneously to mouse model of Der f2 induced allergic asthma and the preventive effects were evaluated. Our results showed that HMSNs were spherical (100 nm) with pore diameter of 2.897 nm and successfully loaded with Der f2 protein. The loading capacity is 90 μg Der f2/1 mg HMSNs. The Der f2 loaded on HMSNs released slowly in 72 h. Treatment with Der f2 loaded HMSNs could efficiently decrease Der f2 specific IgE levels, inflammatory cells infiltration in lung tissue, and Th2 cytokine IL4 levels in BALF. In the meanwhile, it could increase the Der f2 specific IgG levels, Th1 cytokine IFN-γ levels, and induce proliferation of splenocytes to Der f2 accompanied by increased IFN-γ levels. These results showed that Der f2 loaded HMSNs were efficient in preventing allergic inflammation, and HMSNs may be potential vehicles for SIT of HDM allergy.

Tailoring inorganic nanoadjuvants towards next-generation vaccines

Vaccines, one of the most effective and powerful public health measures, have saved countless lives over the past century and still have a tremendous global impact. As an indispensable component of modern vaccines, adjuvants play a critical role in strengthening and/or shaping a specific immune response against infectious diseases as well as malignancies. The application of nanotechnology provides the possibility of precisely tailoring the building blocks of nanoadjuvants towards modern vaccines with the desired immune response. The last decade has witnessed great academic progress in inorganic nanomaterials for vaccine adjuvants in terms of nanometer-scale synthesis, structure control, and functionalization design. Inorganic adjuvants generally facilitate the delivery of antigens, allowing them to be released in a sustained manner, enhance immunogenicity, deliver antigens efficiently to specific targets, and induce a specific immune response. In particular, the recent discovery of the intrinsic immunomodulatory function of inorganic nanomaterials further allows us to shape the immune response towards the desired type and increase the efficacy of vaccines. In this article, we comprehensively review state-of-the-art research on the use of inorganic nanomaterials as vaccine adjuvants. Attention is focused on the physicochemical properties of versatile inorganic nanoadjuvants, such as composition, size, morphology, shape, hydrophobicity, and surface charge, to effectively stimulate cellular immunity, considering that the clinically used alum adjuvants can only induce strong humoral immunity. In addition, the efforts made to date to expand the application of inorganic nanoadjuvants in cancer vaccines are summarized. Finally, we discuss the future prospects and our outlook on tailoring inorganic nanoadjuvants towards next-generation vaccines.

Aluminium adjuvants used in vaccines

This is a protocol for a Cochrane Review (Intervention). The objectives are as follows:

To assess the benefits and harms of aluminium adjuvants used in a vaccine or an excipient versus the same vaccine or excipient, but having a different type of aluminium adjuvant formulation, or a different concentration, or with a different particle size.

Vaccine-induced antigen-specific regulatory T cells attenuate the antiviral immunity against acute influenza virus infection

Peptide-based T cell vaccines targeting the conserved epitopes of influenza virus can provide cross-protection against distantly related strains, but they are generally not immunogenic. Foreign antigen-specific regulatory T (Treg) cells are induced under subimmunogenic conditions peripherally, although their development and role in vaccine-mediated antiviral immunity is unclear. Here, we demonstrated primary vaccination with peptides alone significantly induced antigen-specific Foxp3⁺ Treg cells, which were further expanded by repeated vaccination with unadjuvanted peptides. Certain adjuvants, including CpG, suppressed the induction and expansion of antigen-specific Treg cells by peptide vaccination. Interestingly, secondary influenza virus infection significantly increased the frequency of preexisting antigen-specific Treg cells, although primary infection barely induced them. Importantly, specific depletion of vaccine-induced antigen-specific Treg cells promoted influenza viral clearance, indicating their inhibitory role in vivo. Immunization with CpG-adjuvanted peptides by the subcutaneous prime-intranasal-boost strategy restricted the recruitment and accumulation of antigen-specific Treg cells in lung, and stimulated robust T cell immunity. Finally, subcutaneous prime-intranasal-boost immunization with CpG-adjuvanted peptides or whole-inactivated influenza vaccines protected mice from heterosubtypic influenza virus infection. In conclusion, antigen-specific Treg cells induced by peptide vaccines attenuate the antiviral immunity against influenza virus infection. CpG-adjuvanted peptide vaccines provide heterosubtypic influenza protection probably by inhibiting Treg development and enhancing T cell immunity.

Age-related differences in humoral and cellular immune responses after primary immunisation: indications for stratified vaccination schedules

Immunosenescence is characterised by reduced B and T cell responses. Evidence shows that booster vaccinations are less effective in elderly people, but data on the efficacy of primary immunisation are sparse. We conducted a monocentric, open label, phase IV trial to compare immune responses to primary vaccinations using the inactivated, adjuvanted Japanese Encephalitis vaccine by 30 elderly people (mean 69, range 61-78 years) and 30 younger people (mean 24, range 18-30 years). Humoral and cellular immune responses were analysed in relation to age and cytomegalovirus (CMV) seropositivity. Vaccine-specific antibody titres were significantly lower in elderly participants and 47% of them were non- or low responders after the two doses of the vaccine neo-antigen. The reduced humoral immune responses in elderly people correlated with reduced cytokine production, such as interferon gamma (IFN-γ) in vitro, as well as higher frequencies of late-differentiated effector and effector memory T cells and T regulatory cells. These cellular changes and lower antibody titres were particularly prominent in CMV-seropositive elderly participants. If primary vaccination before the age of 60 is not possible, elderly patients may require different vaccination strategies to ensure sufficient long-lasting immunity, such as adapted or accelerated schedules and the use of different adjuvants.

Uric acid and the vaccine adjuvant activity of aluminium (oxy)hydroxide nanoparticles

In an effort to improve the adjuvanticity of insoluble aluminium salts, we discovered that the adjuvant activity of aluminium salt nanoparticles is significantly stronger than aluminium salt microparticles, likely related to nanoparticle's stronger ability to directly activate NACHT, LRR and PYD domains-containing protein 3 (NLRP3) inflammasome as the nanoparticles are more efficiently taken up by phagocytic cells. Endogenous signals such as uric acid from cell damage or death caused by the cytotoxicity of aluminium salts are thought to indirectly activate inflammasome, prompting us to hypothesise that the potent adjuvant activity of aluminium salt nanoparticles is also related to their ability to stimulate uric acid production. In the present study, we prepared aluminium (oxy)hydroxide nanoparticles (∼ 30-100 nm) and microparticles (X50, 9.43 μm) and showed that intraperitoneal injection of mice with the nanoparticles, absorbed with ovalbumin, led to a significant increase in uric acid level in the peritoneal lavage, whereas the microparticles did not. The aluminium (oxy)hydroxide nanoparticles' ability to stimulate uric acid production was also confirmed in cell culture. We concluded that the stronger adjuvant activity of insoluble aluminium (oxy)hydroxide nanoparticles, relative to microparticles, may be attributed at least in part to their stronger ability to induce endogenous danger signals such as uric acid.

Clay Nanoparticles Elicit Long-Term Immune Responses by Forming Biodegradable Depots for Sustained Antigen Stimulation

Nanomaterials have been widely tested as new generation vaccine adjuvants, but few evoke efficient immunoreactions. Clay nanoparticles, for example, layered double hydroxide (LDH) and hectorite (HEC) nanoparticles, have shown their potent adjuvanticity in generating effective and durable immune responses. However, the mechanism by which clay nanoadjuvants stimulate the immune system is not well understood. Here, it is demonstrated that LDH and HEC-antigen complexes form loose agglomerates in culture medium/serum. They also form nodules with loose structures in tissue after subcutaneous injection, where they act as a depot for up to 35 d. More importantly, clay nanoparticles actively and continuously recruit immune cells into the depot for up to one month, and stimulate stronger immune responses than FDA-approved adjuvants, Alum and QuilA. Sustained antigen release is also observed in clay nanoparticle depots, with 50-60% antigen released after 35 d. In contrast, Alum-antigen complexes show minimal antigen release from the depot. Importantly, LDH and HEC are more effective than QuilA and Alum in promoting memory T-cell proliferation. These findings suggest that both clay nanoadjuvants can serve as active vaccine platforms for sustained and potent immune responses.

Outer Membrane Vesicles: Current Status and Future Direction of These Novel Vaccine Adjuvants

Adjuvants have been of great interest to vaccine formulation as immune-stimulators. Prior to the recent research in the field of immune stimulation, conventional adjuvants utilized for aluminum-based vaccinations dominated the adjuvant market. However, these conventional adjuvants have demonstrated obvious defects, including poor protective efficiency and potential side effects, which hindered their widespread circulation. Outer membrane vesicles (OMVs) naturally exist in gram-negative bacteria and are capable of engaging innate and adaptive immunity and possess intrinsic adjuvant capacity. They have shown tremendous potential for adjuvant application and have recently been successfully applied in various vaccine platforms. Adjuvants could be highly effective with the introduction of OMVs, providing complete immunity and with the benefits of low toxicity; further, OMVs might also be designed as an advanced mucosal delivery vehicle for use as a vaccine carrier. In this review, we discuss adjuvant development, and provide an overview of novel OMV adjuvants and delivery vehicles. We also suggest future directions for adjuvant research. Overall, we believe that OMV adjuvants would find high value in vaccine formulation in the future.

Adjuvant strategies to improve vaccination of the elderly population

Immunosenescence contributes to increased incidence and severity of many infections in old age and is responsible for impaired immunogenicity and efficacy of vaccines. Adjuvants are one strategy to enhance immunogenicity of vaccines. The oil-in-water emulsions MF59TM and AS03, as well as a virosomal vaccine have been licensed in seasonal or pandemic influenza vaccines and are/were used successfully in the elderly. AS01, a liposome-based adjuvant comprising two immunostimulants has recently been approved in a recombinant protein vaccine for older adults, which showed very high efficacy against herpes zoster in clinical trials. Several adjuvants for use in the older population are in clinical and preclinical development and will hopefully improve vaccines for this age group in the future.

Allergic patients with and without allergen-specific immunotherapy mount protective immune responses to tick-borne encephalitis vaccination in absence of enhanced side effects or propagation of their Th2 bias

BACKGROUND

Allergic diseases are caused by Th2-driven immune responses and their treatment with specific immunotherapy (SIT) leads to immunomodulation via IL10, TGF-ß and Th1/Tr1 shift. This phase IV, open-label clinical trial investigated whether allergies and SIT treatment influenced immune responses to routine vaccination.

METHODS

We studied three groups: 49 allergic patients (allergic group), 21 allergic patients receiving maintenance doses of SIT (SIT group), and 49 non-allergic controls. All subjects received tick-borne encephalitis (TBE) booster vaccines and humoral and cellular immune responses were evaluated after one week, four weeks and six months.

RESULTS

The levels and kinetics of neutralizing TBE-specific antibodies, reflecting protection against TBE, were not significantly different in the three groups. The allergic group showed Th2 polarization pre-booster as indicated by increased TBE-specific IgG1 and elevated mitogen-induced IL5 production. Alum-adjuvanted TBE vaccine led to Th2 biased immune responses in the controls, but to no further enhancement of Th2 polarization in the allergic and SIT group. Furthermore, in the SIT group cellular parameters reflected the induction of immunomodulation due to increased Tregs, elevated baseline IL10 and lack of TBE-specific IL5. Importantly, these cellular regulatory responses did not limit the ability to mount sufficient TBE-specific antibodies after the booster. All groups tolerated the vaccine well with no exacerbation of allergic symptoms.

CONCLUSION

TBE booster vaccinations were immunogenic and safe in both the allergic and SIT group and contributed to balanced immune responses. Our data indicate that all allergic patients, even when undergoing SIT, should be vaccinated without hesitation and at regular intervals according to standard recommendations. ClinicalTrials.gov (NCT02511535).

The novel complex combination of alum, CpG ODN and HH2 as adjuvant in cancer vaccine effectively suppresses tumor growth in vivo

Single-component adjuvant is prone to eliciting a specific type of Th1 or Th2 response. So, the development of combinatorial adjuvants inducing a robust mixed Th1/Th2 response is a promising vaccination strategy against cancer. Here, we describe a novel combination of aluminum salts (alum), CpG oligodeoxynucleotide (CpG) and innate defense regulator peptide HH2 for improving anti-tumor immune responses. The CpG-HH2 complex significantly enhanced the production of IFN-γ, TNF-α and IL-1β, promoted the uptake of antigen and strengthened the activation of p38, Erk1/2 and NF-κB in vitro, compared to CpG or HH2 alone. Immunization with NY-ESO-1 antigen plus alum-CpG-HH2 combinatorial adjuvant effectively inhibited tumor growth and reduced tumor burden in prophylactic and therapeutic tumor models and even in passive serum or cellular therapy. In addition, co-administration of NY-ESO-1 with alum-CpG-HH2 combinatorial adjuvant markedly activated NK cell cytotoxicity, induced antibody-dependent cellular cytotoxicity (ADCC), dramatically elicited cytotoxic T lymphocytes (CTLs) response, and increased infiltrating lymphocytes in tumors. Moreover, in vivo depletion of CD8⁺ T cells completely and depletion of NK cells partially blocked the anti-tumor activity of NY-ESO-1-alum-CpG-HH2 immunization. Overall, our results demonstrate a novel adjuvant combination for cancer vaccine with efficient immunomodulation by stimulating innate immunity and mediating adaptive immunity.

Nanoemulsion adjuvant-driven redirection of TH2 immunity inhibits allergic reactions in murine models of peanut allergy

BACKGROUND

Immunotherapy for food allergies involves progressive increased exposures to food that result in desensitization to food allergens in some subjects but not tolerance to the food. Therefore new approaches to suppress allergic immunity to food are necessary. Previously, we demonstrated that intranasal immunization with a nanoemulsion (NE) adjuvant induces robust mucosal antibody and T_H17-polarized immunity, as well as systemic T_H1-biased cellular immunity with suppression of pre-existing T_H2-biased immunity.

OBJECTIVE

We hypothesized that immunization with food in conjunction with the nanoemulsion adjuvant could lead to modulation of allergic reactions in food allergy by altering pre-existing allergic immunity and enhancing mucosal immunity.

METHODS

Mice were sensitized to peanut with aluminum hydroxide or cholera toxin. The animals were then administered 3 monthly intranasal immunizations with peanut in the nanoemulsion adjuvant or saline. Mice were then challenged with peanut to examine allergen reactivity.

RESULTS

The NE intranasal immunizations resulted in marked decreases in T_H2 cytokine, IgG₁, and IgE levels, whereas T_H1 and mucosal T_H17 immune responses were increased. After allergen challenge, these mice showed significant reductions in allergic hypersensitivity. Additionally, the NE immunizations significantly increased antigen-specific IL-10 production and regulatory T-cell counts, and the protection induced by NE was dependent in part on IL-10. Control animals immunized with intranasal peanut in saline had no modulation of their allergic response.

CONCLUSIONS

NE adjuvant-mediated induction of mucosal T_H17 and systemic T_H1-biased immunity can suppress T_H2-mediated allergy through multiple mechanisms and protect against anaphylaxis. These results suggest the potential therapeutic utility of this approach in the setting of food allergy.

Evaluation of the efficacy of a novel porcine circovirus type 2 synthetic peptide vaccine

A novel porcine circovirus type 2 (PCV2) peptide vaccine comprised of a consensus capsid (Cap) protein domain encoded by open reading frame 2 was developed to control PCV2 infection. The efficacy of the vaccine was evaluated against a commercial baculovirus-expressed recombinant PCV2 subunit vaccine based on the Cap protein. The amino acid sequence of this Cap protein was designed based on the alignment of amino acid sequences from different isolates from Europe, North America, and Asia. The vaccine was evaluated in either phosphate-buffered saline or adjuvanted with aluminum hydroxide, cobalt oxide, or liposome. Overall the PCV2 peptide vaccine was less efficacious against PCV2 challenge compared with the commercial PCV2 vaccine. The peptide vaccine was the most efficacious when liposome was used as an adjuvant, significantly (P < 0.05) reducing viremia while increasing the levels of neutralizing antibodies and interferon-γ secreting cells. This suggests, in the presence of liposome, the peptide vaccine was able to elicit both humoral and cellular immune responses.

Immunotherapy approach with recombinant survivin adjuvanted with alum and MIP suppresses tumor growth in murine model of breast cancer

Survivin has received attention as a potential target for cancer immunotherapy because of its crucial role in oncogenesis. We undertook this study to evaluate the immunotherapeutic potential of combination of recombinant survivin along with adjuvant alum and immune modulator Mycobacterium indicus pranii (MIP). In vivo efficacy of the combination was studied in an invasive murine breast cancer model. Recombinant survivin protein was purified from Escherichia coli based expression system and characterized by western blotting. Purified survivin protein was combined with alum and MIP and was used for immunization of Balb/c mice. Antigen-primed animals were then challenged with syngeneic mammary tumor cells known as 4T-1. Balb/c mice spontaneously develop tumor when inoculated with 4T-1 cells. Antigen and adjuvant combination was immunogenic and significantly suppressed tumor growth in mice immunized with combination of recombinant survivin (10 µg), alum, and MIP. This is the first report that describes a combination immunotherapy approach using recombinant survivin, alum, and MIP in highly metastatic murine breast cancer model and holds promise for development of new biotherapeutics for cancer.

Development of nanoparticle adjuvants to potentiate the immune response against diphtheria toxoid

BACKGROUND

Over the years, diphtheria was known as contagious fatal infection caused by Corynebacterium diphtheria that affects upper respiratory system. The spread of diphtheria epidemic disease is best prevented by vaccination with diphtheria toxoid vaccine. Aluminum adjuvants were reported to stimulate the immune responses to killed and subunit vaccines.

OBJECTIVE

Our study aimed to minimize adjuvant particles size, to gain insight of resulting immunity titer and impact on immune response antibody subtypes.

METHODS

Aluminum salts and calcium phosphate adjuvants were prepared, followed by micro/nanoparticle adjuvants preparation. After formulation of diphtheria vaccine from diphtheria toxoid and developed adjuvants, we evaluated efficacy of these prepared vaccines based on their impact on immune response via measuring antibodies titer, antibodies isotyping and cytokines profile in immunized mice.

RESULTS

A noteworthy increase in immunological parameters was observed; antibodies titer was higher in serum of mice injected with nanoparticle adjuvants-containing vaccine than mice injected with standard adjuvant-containing vaccine and commercial vaccine. Aluminum compounds adjuvants (nanoparticles and microparticles formulation) and microparticles calcium phosphate adjuvant induce TH2 response, while nanoparticles calcium phosphate and microparticles aluminum compounds adjuvants stimulate TH1 response.

CONCLUSIONS

Different treatments to our adjuvant preparations (nanoparticles and microparticles formulation) had a considerable impact on vaccine immunogenicity.

Adjuvanted influenza vaccines

In spite of current influenza vaccines being immunogenic, evolution of the influenza virus can reduce efficacy and so influenza remains a major threat to public health. One approach to improve influenza vaccines is to include adjuvants; substances that boost the immune response. Adjuvants are particularly beneficial for influenza vaccines administered during a pandemic when a rapid response is required or for use in patients with impaired immune responses, such as infants and the elderly. This review outlines the current use of adjuvants in human influenza vaccines, including what they are, why they are used and what is known of their mechanism of action. To date, six adjuvants have been used in licensed human vaccines: Alum, MF59, AS03, AF03, virosomes and heat labile enterotoxin (LT). In general these adjuvants are safe and well tolerated, but there have been some rare adverse events when adjuvanted vaccines are used at a population level that may discourage the inclusion of adjuvants in influenza vaccines, for example the association of LT with Bell's Palsy. Improved understanding about the mechanisms of the immune response to vaccination and infection has led to advances in adjuvant technology and we describe the experimental adjuvants that have been tested in clinical trials for influenza but have not yet progressed to licensure. Adjuvants alone are not sufficient to improve influenza vaccine efficacy because they do not address the underlying problem of mismatches between circulating virus and the vaccine. However, they may contribute to improved efficacy of next-generation influenza vaccines and will most likely play a role in the development of effective universal influenza vaccines, though what that role will be remains to be seen.

Opinion: Making Inactivated and Subunit-Based Vaccines Work

Empirically derived vaccines have in the past relied on the isolation and growth of disease-causing microorganisms that are then inactivated or attenuated before being administered. This is often done without prior knowledge of the mechanisms involved in conferring protective immunity. Recent advances in scientific technologies and in our knowledge of how protective immune responses are induced enable us to rationally design novel and safer vaccination strategies. Such advances have accelerated the development of inactivated whole-organism- and subunit-based vaccines. In this review, we discuss ideal attributes and criteria that need to be considered for the development of vaccines and some existing vaccine platforms. We focus on inactivated vaccines against influenza virus and ways by which vaccine efficacy can be improved with the use of adjuvants and Toll-like receptor-2 signaling.

Effect of apoptosis-associated speck-like protein containing a caspase recruitment domain on vaccine efficacy: Overcoming the effects of its deficiency with aluminum hydroxide adjuvant

Host factors such as nutritional status and immune cell state are important for vaccine efficacy. Inflammasome activation may be important for triggering vaccine-induced humoral and cell-mediated immune responses. Formulations with alum as a typical adjuvant to overcome the effects of host factors have recently been shown to induce inflammasome activation, which augments vaccine efficacy. Apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) is one of the main components of inflammasomes, but it is not clear whether ASC affects the vaccine-induced immune response. Herein, we used two types of vaccines: inactivated influenza vaccine not formulated with alum, and HPV vaccine formulated with alum. We gave the vaccines to ASC knockout (ASC^-/- ) mice to investigate the role of ASC in vaccine efficacy. Influenza vaccine-immunized ASC^-/- mice did not show antibody titers in week 2 after the first vaccination. After boosting, the antibody titer in ASC^-/- mice was about half that in wild type (WT) mice. Furthermore, a cytotoxic T-lymphocyte response against influenza vaccine was not induced in ASC^-/- mice. Therefore, vaccinated ASC^-/- mice did not show effective protection against viral challenge. ASC^-/- mice immunized with alum-formulated HPV vaccine showed similar antibody titers and T-cell proliferation compared with immunized WT mice. However, the HPV vaccine without alum induced up to threefold lower titers of HPV-specific antibody titers in ASC^-/- mice compared with those in WT mice. These findings suggest that alum in vaccine can overcome the ASC-deficient condition.