Detoxification of endotoxin by aluminum hydroxide adjuvant

Safety Assessment: a Comparative Analysis of Quantitative Content of Bacterial Endotoxins and Evaluation of Pyrogenicity of the Kazakhstan Vaccine QazCovid-in® against COVID-19

We measured the levels of bacterial endotoxins in the bulk vaccine product (BVP) and finished vaccine QazCovid-in® and evaluated the effect of aluminum hydroxide (adjuvant) on the results of LAL test and pyrogenicity of samples in vivo (in rabbits receiving intravenous injection into the marginal ear vein). Administration of BVP with LPS resulted in a dose-dependent increase in body temperature in rabbits similar to that caused by LPS alone, which suggests that aluminum hydroxide in the vaccine did not affect the pyrogenic response in rabbits. Moreover, the LAL test showed that the aluminum hydroxide did not hinder LPS activity after serial dilution of samples.

Veterinary Autogenous Vaccines for Poultry in Europe-Many Ways to Crack an Egg

In the past decade, European animal farming has increasingly used autogenous vaccines for the prevention of nonnotifiable diseases. In Europe, these vaccines are exclusively inactivated bacterial and viral vaccines, with a set of specific regulations that differentiate them from conventional vaccines. The highest number of applications most likely occurs in poultry, as these animal species are farmed in the highest numbers compared with other types of food-producing animals. In 2019, autogenous vaccines came within the scope of harmonized European regulation for the first time, although many important aspects are still missing and need to be further developed. Consequently, several important legal provisions remain in national legislations and can vary tremendously between different member states of the European Union. The inclusion of autogenous vaccines in the management of certain diseases of poultry is justified by the nonavailability of licensed vaccines and the evolution and diversity of antigens in the field that are not covered by licensed vaccines. In addition, these vaccines aid in reducing the use of antibiotics. The methods for isolating and typing pathogenic isolates to obtain relevant antigens are pathogen specific and require a careful approach based on clinical evidence. Manufacturing processes are optimized according to regulatory standards, and they represent the most critical factor influencing the quality of autogenous vaccines and their placement on the market. This review presents the important requirements for manufacturing autogenous vaccines for poultry in addition to the relevant regulatory considerations. The results from a survey of several European Union member states regarding specific provisions within their national legislations are also presented.

Co-delivery of a trimeric spike DNA and protein vaccine with aluminum hydroxide enhanced Th1-dominant humoral and cellular immunity against SARS-CoV-2

Protein subunit vaccines have been used as prophylactic vaccines for a long time. The well-established properties of these vaccines make them the first choice for the coronavirus disease 2019 (COVID-19) outbreak. However, it is not easy to develop a protein vaccine that induces cytotoxic T lymphocyte responses and requires a longer time for manufacturing, which limits the usage of this vaccine type. Here, we report the combination of a recombinant spike (S)-trimer protein with a DNA vaccine-encoded S protein as a novel COVID-19 vaccine. The recombinant S protein was formulated with different adjuvants and mixed with the DNA plasmid before injection. We found that the recombinant S protein formulated with the adjuvant aluminum hydroxide and mixed with the DNA plasmid could enhance antigen-specific antibody titers, neutralizing antibody titers. We further evaluated the IgG2a/IgG1 isotype and cytokine profiles of the specific boosted T-cell response, which indicated that the combined vaccine induced a T-helper 1 cell-biased immune response. Immunized hamsters were challenged with severe acute respiratory syndrome coronavirus 2, and the body weight of the hamsters that received the recombinant S protein with aluminum hydroxide and/or the DNA plasmid was not reduced. Alternatively, those that received control or only the DNA plasmid immunization were reduced. Interestingly, after the third day of the viral load in the lungs, the viral challenge could not be detected in hamsters immunized with the recombinant S protein in aluminum hydroxide mixed with DNA (tissue culture infectious dose < 10). The viral load in the lungs was 109 , 106 , and 107 for the phosphate-buffered saline, protein in aluminum hydroxide, and DNA-only immunizations, respectively. These results indicated that antiviral mechanisms neutralizing antibodies play important roles. Furthermore, we found that the combination of protein and DNA vaccination could induce relatively strong CD8+ T-cell responses. In summary, the protein subunit vaccine combined with a DNA vaccine could induce strong CD8+ T-cell responses to increase antiviral immunity for disease control.

Aluminum Adjuvants-'Back to the Future'

Aluminum-based adjuvants will continue to be a key component of currently approved and next generation vaccines, including important combination vaccines. The widespread use of aluminum adjuvants is due to their excellent safety profile, which has been established through the use of hundreds of millions of doses in humans over many years. In addition, they are inexpensive, readily available, and are well known and generally accepted by regulatory agencies. Moreover, they offer a very flexible platform, to which many vaccine components can be adsorbed, enabling the preparation of liquid formulations, which typically have a long shelf life under refrigerated conditions. Nevertheless, despite their extensive use, they are perceived as relatively 'weak' vaccine adjuvants. Hence, there have been many attempts to improve their performance, which typically involves co-delivery of immune potentiators, including Toll-like receptor (TLR) agonists. This approach has allowed for the development of improved aluminum adjuvants for inclusion in licensed vaccines against HPV, HBV, and COVID-19, with others likely to follow. This review summarizes the various aluminum salts that are used in vaccines and highlights how they are prepared. We focus on the analytical challenges that remain to allowing the creation of well-characterized formulations, particularly those involving multiple antigens. In addition, we highlight how aluminum is being used to create the next generation of improved adjuvants through the adsorption and delivery of various TLR agonists.

Research Progress of Aluminum Phosphate Adjuvants and Their Action Mechanisms

Although hundreds of different adjuvants have been tried, aluminum-containing adjuvants are by far the most widely used currently. It is worth mentioning that although aluminum-containing adjuvants have been commonly applied in vaccine production, their acting mechanism remains not completely clear. Thus far, researchers have proposed the following mechanisms: (1) depot effect, (2) phagocytosis, (3) activation of pro-inflammatory signaling pathway NLRP3, (4) host cell DNA release, and other mechanisms of action. Having an overview on recent studies to increase our comprehension on the mechanisms by which aluminum-containing adjuvants adsorb antigens and the effects of adsorption on antigen stability and immune response has become a mainstream research trend. Aluminum-containing adjuvants can enhance immune response through a variety of molecular pathways, but there are still significant challenges in designing effective immune-stimulating vaccine delivery systems with aluminum-containing adjuvants. At present, studies on the acting mechanism of aluminum-containing adjuvants mainly focus on aluminum hydroxide adjuvants. This review will take aluminum phosphate as a representative to discuss the immune stimulation mechanism of aluminum phosphate adjuvants and the differences between aluminum phosphate adjuvants and aluminum hydroxide adjuvants, as well as the research progress on the improvement of aluminum phosphate adjuvants (including the improvement of the adjuvant formula, nano-aluminum phosphate adjuvants and a first-grade composite adjuvant containing aluminum phosphate). Based on such related knowledge, determining optimal formulation to develop effective and safe aluminium-containing adjuvants for different vaccines will become more substantiated.

Dectin-1 signaling coordinates innate and adaptive immunity for potent host defense against viral infection

Background

Most commercial foot-and-mouth disease (FMD) vaccines have various disadvantages, such as low antibody titers, short-lived effects, compromised host defense, and questionable safety.

Objectives

To address these shortcomings, we present a novel FMD vaccine containing Dectin-1 agonist, β-D-glucan, as an immunomodulatory adjuvant. The proposed vaccine was developed to effectively coordinate innate and adaptive immunity for potent host defense against viral infection.

Methods

We demonstrated β-D-glucan mediated innate and adaptive immune responses in mice and pigs in vitro and in vivo. The expressions of pattern recognition receptors, cytokines, transcription factors, and co-stimulatory molecules were promoted via FMD vaccine containing β-D-glucan.

Results

β-D-glucan elicited a robust cellular immune response and early, mid-, and long-term immunity. Moreover, it exhibited potent host defense by modulating host's innate and adaptive immunity.

Conclusion

Our study provides a promising approach to overcoming the limitations of conventional FMD vaccines. Based on the proposed vaccine's safety and efficacy, it represents a breakthrough among next-generation FMD vaccines.

Modulation of Skin Inflammatory Responses by Aluminum Adjuvant

Aluminum salt (AS), one of the most commonly used vaccine adjuvants, has immuno-modulatory activity, but how the administration of AS alone may impact the activation of the skin immune system under inflammatory conditions has not been investigated. Here, we studied the therapeutic effect of AS injection on two distinct skin inflammatory mouse models: an imiquimod (IMQ)-induced psoriasis-like model and an MC903 (calcipotriol)-induced atopic dermatitis-like model. We found that injection of a high dose of AS not only suppressed the IMQ-mediated development of T-helper 1 (Th1) and T-helper 17 (Th17) immune responses but also inhibited the IMQ-mediated recruitment and/or activation of neutrophils and macrophages. In contrast, AS injection enhanced MC903-mediated development of the T-helper 2 (Th2) immune response and neutrophil recruitment. Using an in vitro approach, we found that AS treatment inhibited Th1 but promoted Th2 polarization of primary lymphocytes, and inhibited activation of peritoneal macrophages but not bone marrow derived neutrophils. Together, our results suggest that the injection of a high dose of AS may inhibit Th1 and Th17 immune response-driven skin inflammation but promote type 2 immune response-driven skin inflammation. These results may provide a better understanding of how vaccination with an aluminum adjuvant alters the skin immune response to external insults.

Exploration of Pattern Recognition Receptor Agonists as Candidate Adjuvants

Adjuvants are used to maximize the potency of vaccines by enhancing immune reactions. Components of adjuvants include pathogen-associated molecular patterns (PAMPs) and damage-associate molecular patterns (DAMPs) that are agonists for innate immune receptors. Innate immune responses are usually activated when pathogen recognition receptors (PRRs) recognize PAMPs derived from invading pathogens or DAMPs released by host cells upon tissue damage. Activation of innate immunity by PRR agonists in adjuvants activates acquired immune responses, which is crucial to enhance immune reactions against the targeted pathogen. For example, agonists for Toll-like receptors have yielded promising results as adjuvants, which target PRR as adjuvant candidates. However, a comprehensive understanding of the type of immunological reaction against agonists for PRRs is essential to ensure the safety and reliability of vaccine adjuvants. This review provides an overview of the current progress in development of PRR agonists as vaccine adjuvants, the molecular mechanisms that underlie activation of immune responses, and the enhancement of vaccine efficacy by these potential adjuvant candidates.

The tug of war between Al3+ and Na+ for order-disorder transitions in lipid-A membranes

Cations play a critical role in the stability and morphology of lipid-A aggregates by neutralizing, hydrating and cross-linking these glycolipid molecules. Monophosphorylated lipid-A is the major immunostimulatory principle in commercially available adjuvants containing Al3+ such as adjuvant system 04 (AS04). The antagonist/agonist immunomodulatory properties of lipid-A are associated with chemical variations (e.g. the number of acyl chains and phosphate groups) and their aggregate arrangements (e.g. lamellar, nonlamellar or mixed). Therefore, the identification of the active form of lipid-A can provide valuable guidance in the development of vaccine adjuvants capable of boosting the immune system with decreased reactogenicity. Although the effect of mono and divalent cations on the structural polymorphism and endotoxicity of LPS has been previously investigated, much less is known about the effect of trivalent cations. We have investigated the effect of NaCl and AlCl3 salt solutions on the structural dynamics and stability of mono and diphosphorylated lipid-A membranes via atomistic MD simulations. The Al3+ ion exerts two major effects on the structural dynamics of lipid-A membranes. It acts as an efficient cross-linker of mono or diphosphorylated lipid-A molecules, thus stabilizing the lamellar arrangement of these glycolipids. It also alters the lipid-A packing and membrane fluidity, inducing disorder → order structural transitions of the membrane. This effect is promptly reversed upon the addition of NaCl solution, which promotes a nearly threefold increase in the amount of water in the carbohydrate moiety of the Al3+-containing lipid-A membranes. The exchange dynamics and residence times of cation-coordinated water molecules in these membranes provide insights into the molecular mechanism for the Na+-induced transition from a densely packed ordered phase to a disordered one. Al3+ counter-ions favor ordered lamellar aggregates, which has been previously associated with the lack of endotoxic activity and cytokine-inducing action. The resulting microscopic understanding of the structure and dynamics of lipid-A aggregates in the presence of Al3+ and Na+ salts can provide valuable guidance in the development of vaccine adjuvants capable of boosting the immune system with decreased reactogenicity.

Development of a Monocyte Activation Test as an Alternative to the Rabbit Pyrogen Test for Mono- and Multi-Component Shigella GMMA-Based Vaccines

Generalised modules for membrane antigens (GMMA)-based vaccines comprise the outer membrane from genetically modified Gram-negative bacteria containing membrane proteins, phospholipids and lipopolysaccharides. Some lipoproteins and lipopolysaccharides are pyrogens; thus, GMMA-based vaccines are intrinsically pyrogenic. It is important to control the pyrogenic content of biological medicines, including vaccines, to prevent adverse reactions such as febrile responses. The rabbit pyrogen test (RPT) and bacterial endotoxin test (BET) are the most commonly employed safety assays used to detect pyrogens. However, both tests are tailored for detecting pyrogenic contaminants and have considerable limitations when measuring the pyrogen content of inherently pyrogenic products. We report the adaptation of the monocyte activation test (MAT) as an alternative to the RPT for monitoring the pyrogenicity of Shigella GMMA-based vaccines. The European Pharmacopoeia endorses three MAT methods (A–C). Of these, method C, the reference lot comparison test, was identified as the most suitable. This method was evaluated with different reference materials to ensure parallelism and consistency for a mono- and multi-component Shigella GMMA vaccine. We demonstrate the drug substance as a promising reference material for safety testing of the matched drug product. Our results support the implementation of MAT as an alternative to the RPT and use of the defined parameters can be extended to GMMA-based vaccines currently in development, aiding vaccine batch release.

Lipopolysaccharide removal affinity matrices based on novel cationic amphiphilic peptides

Lipopolysaccharide (LPS) is one of the most challenging contaminants in biopharmaceutical industries. Cationic amphiphilic peptides (CAPs) -based affinity matrices can be potent tools for LPS removal in such situations. In this study, two newly designed CAPs derived from the LPS binding site of factor C of horseshoe crab S3E3 and S3E3A were immobilized chemo-selectively on diaminodipropylamine (DADPA) and iodoacetyl functionalized Sepharose beads. Both peptides were immobilized via their carboxyl or sulfhydryl (thiol) groups by amide or thioether bonds, respectively. The generated four affinity matrices were used to remove LPS from bovine serum albumin (BSA). The effects of different influential factors including pH, NaCl, Ethylenediaminetetraacetic acid (EDTA), and LPS concentrations on LPS removal efficiency and protein recovery were investigated by Plackett Burman (PB) method.Statistical analysis revealed that immobilized S3E3 removed LPS more effectively than immobilized S3E3A. Increasing pH and LPS concentration had negative effects on LPS removal efficiency and protein recovery. Increasing NaCl concentration improved protein recovery but reduced LPS removal efficiency. Other factors such as EDTA and type of buffer had no significant effect on the measured responses.

Safety and efficacy of a novel inactivated trivalent Salmonella enterica vaccine in chickens

Food poisoning in humans caused by Salmonella enterica remains a significant global public health concern, with the majority of infections associated with the consumption of contaminated eggs or poultry products. The safety and efficacy of a novel inactivated trivalent Salmonella enterica vaccine containing in addition to Salmonella serovars Enteritidis (O:9, serogroup D) and Typhimurium (O:4, serogroup B) also serovar Infantis (O:7, serogroup C1) formulated with an aluminium hydroxide-gel adjuvant was evaluated under field conditions. A total of 10,229 broiler breeder pullets, housed under commercial conditions, were vaccinated at 10 and 17 weeks of age by the intramuscular route in the breast muscle. The vaccine was safe with no local or systemic reactions or adverse effects on bird performance related to the vaccine detected. Vaccination resulted in notable increases in serovar specific antibodies that were maintained until at least 56 weeks of age. Vaccinated birds subjected to homologous challenges around onset of lay showed significantly reduced faecal shedding and organ invasion. Following heterologous challenge with S. Hadar (O:8, serogroup C2) faecal shedding was significantly reduced. These results demonstrate that this novel vaccine could play a significant role in a comprehensive Salmonella control programme intended to reduce both the incidence of food poisoning in humans and the use of antibiotics during poultry production.

Large-scale production, purification, and function of a tumor multi-epitope vaccine: Peptibody with bFGF/VEGFA

In tumor tissue, basic fibroblast growth factor (bFGF) and vascular endothelial growth factor A (VEGFA) promote tumorigenesis by activating angiogenesis, but targeting single factor may produce drug resistance and compensatory angiogenesis. The Peptibody with bFGF/VEGFA was designed to simultaneously blockade these two factors. We were aiming to produce this Fc fusion protein in a large scale. The biological characterizations of Peptibody strains were identified as Escherichia coli and the fermentation mode was optimized in the shake flasks and 10-L bioreactor. The fermentation was scaled up to 100 L, with wet cell weight (WCW) 126 g/L, production 1.41 g/L, and productivity 0.35 g/(L·h) of IPTG induction. The target protein was isolated by cation-exchange, hydrophobic and Protein A chromatography, with total recovery of 60.28% and HPLC purity of 86.71%. The host cells protein, DNA, and endotoxin residues were within the threshold. In mouse model, immunization of Peptibody vaccine could significantly suppressed the tumor growth and angiogenesis, with inhibition rate of 57.73 and 39.34%. The Peptibody vaccine could elicit high-titer anti-bFGF and anti-VEGFA antibodies, which inhibited the proliferation and migration of Lewis lung cancer cell cells by decreasing the Akt/MAPK signal pathways. Therefore, the Peptibody with bFGF/VEGFA might be used as a therapeutic tumor vaccine. The large-scale process we developed could support its industrial production and pre-clinical study in the future.

Safety and immunogenicity of an alum-adjuvanted whole-virion H7N9 influenza vaccine: a randomized, blinded, clinical trial

OBJECTIVES

A case of H7N9 influenza virus infection was first identified in China in 2013. This virus is considered to have high pandemic potential. Here we developed an H7N9 influenza vaccine containing an aluminium adjuvant and evaluated the safety and immunogenicity of the vaccine.

METHODS

From October 2017 through August 2018 we conducted a randomized, double-blinded, single-centre phase I clinical trial in China among 360 participants aged ≥12 years. All participants received two doses of the vaccine (7.5, 15 or 30 μg haemagglutinin antigen) or placebo at an interval of 21 days. Adverse event data were collected for 30 days after vaccination. Serum samples were collected on days 0, 21 and 42 for the haemagglutinin inhibition (HI) antibody assay.

RESULTS

A total of 347 participants (347/360, 96.4%) completed the study. The proportions of vaccine-related adverse events after one injection were 56.7% (34/60) in the 7.5-μg group, 86.7% (52/60) in the 15-μg group and 86.7% (52/60) in the 30-μg group. The proportions of adverse events after two injections were less than those reported after the first dose. None of the serious adverse events were related to the vaccine. After receiving two doses of the 7.5-μg vaccine, the proportion of participants achieving an HI titre of ≥40 was 98.2% (55/56, 95%CI 72.3~100.0%), with a geometric mean titre (GMT) of 192.6 (95%CI 162.9~227.8).

CONCLUSIONS

The alum-adjuvanted H7N9 whole-virion inactivated vaccine was safe and strongly immunogenic in a population aged ≥12 years.

Adjuvants: What a Difference 15 Years Makes!

Vaccination is a critical tool in modern animal production and key to maintaining animal health. Adjuvants affect the immune response by increasing the rate, quantity, or quality of the protective response generated by the target antigens. Although adjuvant technology dates back to the nineteenth century, there was relatively little improvement in adjuvant technology before the late twentieth century. With the discovery of molecular pathways that regulate the timing, quantity, and quality of the immune response, new technologies are focused on bringing safer, more effective, and inexpensive adjuvants to commercial use.

PolyBall: A new adsorbent for the efficient removal of endotoxin from biopharmaceuticals

The presence of endotoxin, also known as lipopolysaccharides (LPS), as a side product appears to be a major drawback for the production of certain biomolecules that are essential for research, pharmaceutical, and industrial applications. In the biotechnology industry, gram-negative bacteria (e.g., Escherichia coli) are widely used to produce recombinant products such as proteins, plasmid DNAs and vaccines. These products are contaminated with LPS, which may cause side effects when administered to animals or humans. Purification of LPS often suffers from product loss. For this reason, special attention must be paid when purifying proteins aiming a product as free as possible of LPS with high product recovery. Although there are a number of methods for removing LPS, the question about how LPS removal can be carried out in an efficient and economical way is still one of the most intriguing issues and has no satisfactory solution yet. In this work, polymeric poly-ε-caprolactone (PCL) nanoparticles (NPs) (dP = 780 ± 285 nm) were synthesized at a relatively low cost and demonstrated to possess sufficient binding sites for LPS adsorption and removal with ~100% protein recovery. The PCL NPs removed greater than 90% LPS from protein solutions suspended in water using only one milligram (mg) of NPs, which was equivalent to ~1.5 × 106 endotoxin units (EU) per mg of particle. The LPS removal efficacy increased to a higher level (~100%) when phosphate buffered saline (PBS containing 137 mM NaCl) was used as a protein suspending medium in place of water, reflecting positive effects of increasing ionic strength on LPS binding interactions and adsorption. The results further showed that the PCL NPs not only achieved 100% LPS removal but also ~100% protein recovery for a wide concentration range from 20-1000 μg/ml of protein solutions. The NPs were highly effective in different buffers and pHs. To scale up the process further, PCL NPs were incorporated into a supporting cellulose membrane which promoted LPS adsorption further up to ~100% just by running the LPS-containing water through the membrane under gravity. Its adsorption capacity was 2.8 × 106 mg of PCL NPs, approximately 2 -fold higher than that of NPs alone. This is the first demonstration of endotoxin separation with high protein recovery using polymer NPs and the NP-based portable filters, which provide strong adsorptive interactions for LPS removal from protein solutions. Additional features of these NPs and membranes are biocompatible (environment friendly) recyclable after repeated elution and adsorption with no significant changes in LPS removal efficiencies. The results indicate that PCL NPs are an effective LPS adsorbent in powder and membrane forms, which have great potential to be employed in large-scale applications.

Unraveling the enigma: elucidating the relationship between the physicochemical properties of aluminium-based adjuvants and their immunological mechanisms of action

Aluminium salts are by far the most commonly used adjuvants in vaccines. There are only two aluminium salts which are used in clinically-approved vaccines, Alhydrogel® and AdjuPhos®, while the novel aluminium adjuvant used in Gardasil® is a sulphated version of the latter. We have investigated the physicochemical properties of these two aluminium adjuvants and specifically in milieus approximating to both vaccine vehicles and the composition of injection sites. Additionally we have used a monocytic cell line to establish the relationship between their physicochemical properties and their internalisation and cytotoxicity. We emphasise that aluminium adjuvants used in clinically approved vaccines are chemically and biologically dissimilar with concomitantly potentially distinct roles in vaccine-related adverse events.

Optimizing the utilization of aluminum adjuvants in vaccines: you might just get what you want

Aluminum-containing adjuvants have been used for over 90 years to enhance the immune response to vaccines. Recent work has significantly advanced our understanding of the physical, chemical, and biological properties of these adjuvants, offering key insights on underlying mechanisms. Given the long-term success of aluminum adjuvants, we believe that they should continue to represent the “gold standard” against which all new adjuvants should be compared. New vaccine candidates that require adjuvants to induce a protective immune responses should first be evaluated with aluminum adjuvants before other more experimental approaches are considered, since use of established adjuvants would facilitate both clinical development and the regulatory pathway. However, the continued use of aluminum adjuvants requires an appreciation of their complexities, in combination with access to the necessary expertise to optimize vaccine formulations. In this article, we will review the properties of aluminum adjuvants and highlight those elements that are critical to optimize vaccine performance. We will discuss how other components (excipients, TLR ligands, etc.) can affect the interaction between adjuvants and antigens, and impact the potency of vaccines. This review provides a resource and guide, which will ultimately contribute to the successful development of newer, more effective and safer vaccines.

Comparative effectiveness of H7N9 vaccines in healthy individuals

BACKGROUND

Avian H7N9 influenza viruses possess a potential pandemic threat to public health worldwide, and have caused severe infection and high mortality in humans. A series of clinical trials of H7N9 vaccines have been completed. Meta-analyses need to be performed to assess the immunogenicity and safety of H7N9 vaccines.

METHODS

Database research with defined selection criteria was conducted in PubMed, Cochrane Central Register of Controlled Trials, the World Health Organization's International Clinical Trials Registry Platform, ClinicalTrials.gov, etc. Data from randomized clinical trials regarding the immunogenicity and safety of H7N9 vaccines were collected and meta-analyzed.

RESULTS

For non-adjuvanted H7N9 vaccines, high dose formulations induced limited immunogenicity and increased the risk of local and systemic adverse events, simultaneously. For adjuvanted H7N9 vaccines, on the one hand, ISCOMATRIX, MF59, AS03 and aluminium adjuvants applied in H7N9 vaccines could improve immune responses effectively, and non-aluminium adjuvants had superior performance in saving vaccine dose; on the other hand, aluminium adjuvant had the advantages of safety amongst these adjuvants applied in H7N9 vaccines.

CONCLUSION

H7N9 influenza vaccines with adjuvant might represent the optimal available option in an influenza pandemic, at present.

Boehmite and Gibbsite Nanoplates for the Synthesis of Advanced Alumina Products

Boehmite (γ-AlOOH) and gibbsite (α-Al-(OH)3) are important archetype (oxy)hydroxides of aluminum in nature that also play diverse roles across a plethora of industrial applications. Developing the ability to understand and predict the properties and characteristics of these materials, on the basis of their natural growth or synthesis pathways, is an important fundamental science enterprise with wide-ranging impacts. The present study describes bulk and surface characteristics of these novel materials in comprehensive detail, using a collectively sophisticated set of experimental capabilities, including a range of conventional laboratory solids analyses and national user facility analyses such as synchrotron X-ray absorption and scattering spectroscopies as well as small-angle neutron scattering. Their thermal stability is investigated using in situ temperature-dependent Raman spectroscopy. These pure and effectively defect-free materials are ideal for synthesis of advanced alumina products.

Mechanisms of Antigen Adsorption Onto an Aluminum-Hydroxide Adjuvant Evaluated by High-Throughput Screening

The adsorption mechanism of antigen on aluminum adjuvant can affect antigen elution at the injection site and hence the immune response. Our aim was to evaluate adsorption onto aluminum hydroxide (AH) by ligand exchange and electrostatic interactions of model proteins and antigens, bovine serum albumin (BSA), β-casein, ovalbumin (OVA), hepatitis B surface antigen, and tetanus toxin (TT). A high-throughput screening platform was developed to measure adsorption isotherms in the presence of electrolytes and ligand exchange by a fluorescence-spectroscopy method that detects the catalysis of 6,8-difluoro-4-methylumbelliferyl phosphate by free hydroxyl groups on AH. BSA adsorption depended on predominant electrostatic interactions. Ligand exchange contributes to the adsorption of β-casein, OVA, hepatitis B surface antigen, and TT onto AH. Based on relative surface phosphophilicity and adsorption isotherms in the presence of phosphate and fluoride, the capacities of the proteins to interact with AH by ligand exchange followed the trend: OVA < β-casein < BSA < TT. This could be explained by both the content of ligands available in the protein structure for ligand exchange and the antigen's molecular weight. The high-throughput screening platform can be used to better understand the contributions of ligand exchange and electrostatic attractions governing the interactions between an antigen adsorbed onto aluminum-containing adjuvant.

Mineral Adjuvants∗∗The present chapter is an updated version of the chapter “Mineral Adjuvants,” published in Immunopotentiators in Modern Vaccines, p. 217–233. Ed. Virgil Schijns & Derek O'Hagan, Elsevier Science Publishers (2005)

Mineral adjuvants comprise aluminum hydroxide and phosphate adjuvants as well as calcium phosphate adjuvants. In particular, the aluminum salts have achieved an undisputed status as the most commonly used adjuvants in human and veterinary vaccines. Calcium phosphate adjuvant, later discovered by Edgar Relyveld, constitutes a very interesting alternative and has also been applied both in human and veterinary vaccines. New analytical tools applied in adjuvant research are about to take us to the next level of understanding mineral adjuvants. These tools have been used to characterize mineral adjuvants, but so far, in particular, aluminum-based adjuvants in terms of surface marker expression profiles, isotypic profiles, and cytokine profiles. In the past 10 years, the discovery of adjuvant-mediated induction of the NALP3 inflammasome and its impact on the secretion of interleukin (IL)-1β and IL-18 as proinflammatory mediators in the early phases of immune response has been described as an important mechanism for the function of these adjuvants.

Bordetella pertussis outer membrane vesicle vaccine confers equal efficacy in mice with milder inflammatory responses compared to a whole-cell vaccine

The demand for improved pertussis vaccines is urgent due to the resurgence of whooping cough. A deeper understanding of the mode of action of pertussis vaccines is required to achieve this improvement. The vaccine-induced effects of a candidate outer membrane vesicle vaccine (omvPV) and a classical protective but reactogenic whole cell vaccine (wPV) were comprehensively compared in mice. The comparison revealed essential qualitative and quantitative differences with respect to immunogenicity and adverse effects for these vaccines. Both vaccines stimulated a mixed systemic Th1/Th2/Th17 response. Remarkably, omvPV evoked higher IgG levels, lower systemic pro-inflammatory cytokine responses and enhanced splenic gene expression than wPV. The omvPV-induced transcriptome revealed gene signatures of the IFN-signaling pathway, anti-inflammatory signatures that attenuate LPS responses, anti-inflammatory metabolic signatures, and IgG responses. Upon intranasal challenge, both immunized groups were equally efficient in clearing Bordetella pertussis from the lungs. This study importantly shows that immunization with omvPV provides a milder inflammatory responses but with equal protection to bacterial colonization and induction of protective antibody and Th1/Th17 type immune responses compared to wPV. These results emphasize the potential of omvPV as a safe and effective next-generation pertussis vaccine.

Manufacturing DTaP-based combination vaccines: industrial challenges around essential public health tools

INTRODUCTION

The manufacture of DTP-backboned combination vaccines is complex, and vaccine quality is evaluated by both batch composition and conformance of manufacturing history. Since their first availability, both the manufacturing regulations for DTP combination vaccines and their demand have evolved significantly. This has resulted in a constant need to modify manufacturing and quality control processes. Areas covered: Regulations that govern the manufacture of complex vaccines can be inconsistent between countries and need to be aligned with the regulatory requirements that apply in all countries of distribution. Changes in product mix and quantities can lead to uncertainty in vaccine supply maintenance. These problems are discussed in the context of the importance of these products as essential public health tools. Expert commentary: Increasing demand for complex vaccines globally has led to problems in supply due to intrinsically complex manufacturing and regulatory procedures. Vaccine manufacturers are fully engaged in the resolution of these challenges, but currently changes in demand need ideally to be anticipated approximately 3 years in advance due to long production cycle times.

Advances in aluminum hydroxide-based adjuvant research and its mechanism

In the past few decades, hundreds of materials have been tried as adjuvant; however, only aluminum-based adjuvants continue to be used widely in the world. Aluminum hydroxide, aluminum phosphate and alum constitute the main forms of aluminum used as adjuvants. Among these, aluminum hydroxide is the most commonly used chemical as adjuvant. In spite of its wide spread use, surprisingly, the mechanism of how aluminum hydroxide-based adjuvants exert their beneficial effects is still not fully understood. Current explanations for the mode of action of aluminum hydroxide-based adjuvants include, among others, the repository effect, pro-phagocytic effect, and activation of the pro-inflammatory NLRP3 pathway. These collectively galvanize innate as well as acquired immune responses and activate the complement system. Factors that have a profound influence on responses evoked by aluminum hydroxide-based adjuvant applications include adsorption rate, strength of the adsorption, size and uniformity of aluminum hydroxide particles, dosage of adjuvant, and the nature of antigens. Although vaccines containing aluminum hydroxide-based adjuvants are beneficial, sometimes they cause adverse reactions. Further, these vaccines cannot be stored frozen. Until recently, aluminum hydroxide-based adjuvants were known to preferentially prime Th2-type immune responses. However, results of more recent studies show that depending on the vaccination route, aluminum hydroxide-based adjuvants can enhance both Th1 as well as Th2 cellular responses. Advances in systems biology have opened up new avenues for studying mechanisms of aluminum hydroxide-based adjuvants. These will assist in scaling new frontiers in aluminum hydroxide-based adjuvant research that include improvement of formulations, use of nanoparticles of aluminum hydroxide and development of composite adjuvants.

Adjuvants in the Driver's Seat: How Magnitude, Type, Fine Specificity and Longevity of Immune Responses Are Driven by Distinct Classes of Immune Potentiators

The mechanism by which vaccine adjuvants enhance immune responses has historically been considered to be the creation of an antigen depot. From here, the antigen is slowly released and provided to immune cells over an extended period of time. This "depot" was formed by associating the antigen with substances able to persist at the injection site, such as aluminum salts or emulsions. The identification of Pathogen-Associated Molecular Patterns (PAMPs) has greatly advanced our understanding of how adjuvants work beyond the simple concept of extended antigen release and has accelerated the development of novel adjuvants. This review focuses on the mode of action of different adjuvant classes in regards to the stimulation of specific immune cell subsets, the biasing of immune responses towards cellular or humoral immune response, the ability to mediate epitope spreading and the induction of persistent immunological memory. A better understanding of how particular adjuvants mediate their biological effects will eventually allow them to be selected for specific vaccines in a targeted and rational manner.

Factors affecting alum-protein interactions

Alum (or aluminum-containing) adjuvants are key components of many vaccines currently on the market. The immuno-potentiation effect of alum adjuvants is presumably due to their interaction with antigens, leading to adsorption on the alum particle surface. Understanding the mechanism of antigen adsorption/desorption and its influencing factors could provide guidance on formulation design and ensure proper in-vivo immuno-potentiation effect. In this paper, surface adsorption of several model proteins on two types of aluminum adjuvants (Alhydrogel(®) and Adjuphos(®)) are investigated to understand the underlying adsorption mechanisms, capacities, and potential influencing factors. It was found that electrostatic interactions are the major driving force for surface adsorption of all the model proteins except ovalbumin. Alhydrogel has a significantly higher adsorption capacity than Adjuphos. Several factors significantly change the adsorption capacity of both Alhydrogel and Adjuphos, including molecular weight of protein antigens, sodium chloride, phosphate buffer, denaturing agents, and size of aluminum particles. These important factors need to be carefully considered in the design of an effective protein antigen-based vaccine.

Vaccine delivery using nanoparticles

Vaccination has had a major impact on the control of infectious diseases. However, there are still many infectious diseases for which the development of an effective vaccine has been elusive. In many cases the failure to devise vaccines is a consequence of the inability of vaccine candidates to evoke appropriate immune responses. This is especially true where cellular immunity is required for protective immunity and this problem is compounded by the move toward devising sub-unit vaccines. Over the past decade nanoscale size (<1000 nm) materials such as virus-like particles, liposomes, ISCOMs, polymeric, and non-degradable nanospheres have received attention as potential delivery vehicles for vaccine antigens which can both stabilize vaccine antigens and act as adjuvants. Importantly, some of these nanoparticles (NPs) are able to enter antigen-presenting cells by different pathways, thereby modulating the immune response to the antigen. This may be critical for the induction of protective Th1-type immune responses to intracellular pathogens. Their properties also make them suitable for the delivery of antigens at mucosal surfaces and for intradermal administration. In this review we compare the utilities of different NP systems for the delivery of sub-unit vaccines and evaluate the potential of these delivery systems for the development of new vaccines against a range of pathogens.

Mechanism of immunopotentiation and safety of aluminum adjuvants

Aluminum-containing adjuvants are widely used in preventive vaccines against infectious diseases and in preparations for allergy immunotherapy. The mechanism by which they enhance the immune response remains poorly understood. Aluminum adjuvants selectively stimulate a Th2 immune response upon injection of mice and a mixed response in human beings. They support activation of CD8 T cells, but these cells do not undergo terminal differentiation to cytotoxic T cells. Adsorption of antigens to aluminum adjuvants enhances the immune response by facilitating phagocytosis and slowing the diffusion of antigens from the injection site which allows time for inflammatory cells to accumulate. The adsorptive strength is important as high affinity interactions interfere with the immune response. Adsorption can also affect the physical and chemical stability of antigens. Aluminum adjuvants activate dendritic cells via direct and indirect mechanisms. Phagocytosis of aluminum adjuvants followed by disruption of the phagolysosome activates NLRP3-inflammasomes resulting in the release of active IL-1β and IL-18. Aluminum adjuvants also activate dendritic cells by binding to membrane lipid rafts. Injection of aluminum-adjuvanted vaccines causes the release of uric acid, DNA, and ATP from damaged cells which in turn activate dendritic cells. The use of aluminum adjuvant is limited by weak stimulation of cell-mediated immunity. This can be enhanced by addition of other immunomodulatory molecules. Adsorption of these molecules is determined by the same mechanisms that control adsorption of antigens and can affect the efficacy of such combination adjuvants. The widespread use of aluminum adjuvants can be attributed in part to the excellent safety record based on a 70-year history of use. They cause local inflammation at the injection site, but also reduce the severity of systemic and local reactions by binding biologically active molecules in vaccines.

Vaccine delivery using nanoparticles

Vaccination has had a major impact on the control of infectious diseases. However, there are still many infectious diseases for which the development of an effective vaccine has been elusive. In many cases the failure to devise vaccines is a consequence of the inability of vaccine candidates to evoke appropriate immune responses. This is especially true where cellular immunity is required for protective immunity and this problem is compounded by the move toward devising sub-unit vaccines. Over the past decade nanoscale size (<1000 nm) materials such as virus-like particles, liposomes, ISCOMs, polymeric, and non-degradable nanospheres have received attention as potential delivery vehicles for vaccine antigens which can both stabilize vaccine antigens and act as adjuvants. Importantly, some of these nanoparticles (NPs) are able to enter antigen-presenting cells by different pathways, thereby modulating the immune response to the antigen. This may be critical for the induction of protective Th1-type immune responses to intracellular pathogens. Their properties also make them suitable for the delivery of antigens at mucosal surfaces and for intradermal administration. In this review we compare the utilities of different NP systems for the delivery of sub-unit vaccines and evaluate the potential of these delivery systems for the development of new vaccines against a range of pathogens.

Comparison of the immune responses to the CIA06-adjuvanted human papillomavirus L1 VLP vaccine with those against the licensed HPV vaccine Cervarix™ in mice

CIA05 is a toll-like receptor (TLR) 4 agonist derived from an Escherichia coli lipopolysaccharide (LPS) mutant and has been shown to have potential as a vaccine adjuvant. In this study, we investigated the immunopotentiating activity of the adjuvant system CIA06, which is comprised of CIA05 and aluminum hydroxide (alum), when used with the human papillomavirus (HPV) L1 virus-like particles (VLPs) vaccine. BALB/c mice were immunized intramuscularly three times at 2-week intervals with HPV16 L1 VLPs alone or in the presence of various combinations of CIA05 and alum, and the immune responses were assessed. We found that the combination of CIA05 and alum at a ratio of 1:50 (designated CIA06B) yielded the highest immune response in terms of serum anti-HPV L1 VLP IgG antibody titers, splenocyte interferon (IFN)-γ secretion, and antigen-specific memory B cell responses. The immunogenicity of the CIA06B-adjuvanted HPV16/18 L1 VLP vaccine was compared with that of the currently licensed HPV vaccine Cervarix™. The CIA06B-adjuvanted vaccine was similar to Cervarix™ with regard to eliciting serum antigen-specific IgG antibodies and virus-neutralizing antibodies but more effective at inducing splenic cytokine production and memory B cells. We also observed that the antigen-specific IgG antibody titers, splenic IFN-γ secretion and memory B cells induced by the CIA06B-adjuvanted HPV vaccine remained high up to 24 weeks post-immunization. Based on these data, we concluded that CIA06B may have potential as an adjuvant in a potent prophylactic vaccine against HPV infection.

Effect of the strength of adsorption of HIV 1 SF162dV2gp140 to aluminum-containing adjuvants on the immune response

The importance of the strength of antigen adsorption by aluminum-containing adjuvants on immunopotentiation was studied using HIV 1 SF162dV2gp140 (gp140), a potential HIV/AIDS antigen. The strengths of adsorption by aluminum hydroxide (AH) adjuvant and aluminum phosphate adjuvant, as measured by the Langmuir adsorptive coefficient, were 1900 and 400 mL/mg, respectively. The strength of adsorption by AH was modified by pretreatment of AH with two different concentrations of potassium dihydrogen phosphate to produce phosphate-treated aluminum hydroxide adjuvants having adsorptive coefficients of 1200 and 800 mL/mg. The four adjuvants were used to prepare vaccines containing either 1 or 10 μg of gp140 per dose. Antibody studies in mice revealed that the presence of an adjuvant increased the immune response in comparison with a solution of gp140 when the dose was 1 μg. Furthermore, the immune response was inversely related to the adsorptive coefficient. In contrast, no significant difference in immunopotentiation was observed between treatments in the presence or absence of an adjuvant when the dose of gp140 was 10 μg. Analysis of the binding of gp140 to CD4 and anti-gp140 monoclonal antibodies by surface plasmon resonance suggests that tight binding induced structural changes in the antigen.

Aluminum adjuvants: preparation, application, dosage, and formulation with antigen

Important new knowledge about the effect of aluminum adjuvants on the immune response in terms of their impact on cytokine profiles, uptake by antigen-presenting cells (APC), and surface marker expression has been published in recent years. However, although the knowledge about these adjuvants is thus more comprehensive now than ever before, the user is often still confined to a more empirical approach when confronted with practical issues when it comes to the handling and use of these adjuvants. In this chapter we have given focus to the user's perspective, discussing practicalities like dosage, temperature stability, relevant monographs, and preparation with antigen.

Bacterial ghosts as adjuvant particles

The development of more advanced and effective vaccines is of great interest in modern medicine. These new-generation vaccines, based on recombinant proteins or DNA, are often less reactogenic and immunogenic than traditional vaccines. Thus, there is an urgent need for the development of new and improved adjuvants. Besides many other immunostimulatory components, the bacterial ghost (BG) system is currently under investigation as a potent vaccine delivery system with intrinsic adjuvant properties. BGs are nonliving cell envelope preparations from Gram-negative cells, devoid of cytoplasmic contents, while their cellular morphology and native surface antigenic structures remain preserved. Owing to the particulate nature of BGs and the fact that they contain many well known immune-stimulating compounds, BGs have the potential to enhance immune responses against ghost-delivered target antigens.

Activation of dendritic cells and induction of CD4(+) T cell differentiation by aluminum-containing adjuvants

Aluminum-containing adjuvants are widely used in licensed human and veterinary vaccines. However, the mechanism by which these adjuvants enhance the immune response and predominantly stimulate a T(H)2 humoral immune response is not well understood. In this study, the effects of aluminum hydroxide and aluminum phosphate adjuvants on antigen presentation, expression of costimulatory molecules and cytokines by mouse dendritic cells (DCs) and the ability of DCs to induce T helper cell differentiation were investigated. Dendritic cells pulsed with ovalbumin (OVA) adsorbed to aluminum-containing adjuvants activated antigen-specific T cells more effectively than DCs pulsed with OVA alone. Aluminum hydroxide adjuvant had a significantly stronger effect than aluminum phosphate adjuvant. Both aluminum-containing adjuvants significantly increased the expression of CD86 on DCs but only aluminum hydroxide adjuvant also induced moderate expression of CD80. Aluminum-containing adjuvants stimulated the release of IL-1beta and IL-18 from DCs via caspase-1 activation. DCs incubated with LPS and OVA induced T(H)1 differentiation of naïve CD4(+) T cells. In contrast, DCs incubated with aluminum/OVA activated CD4(+) T cells to secrete IL-4 and IL-5 as well as IFN-gamma. Addition of neutralizing anti-IL-1beta antibodies decreased IL-5 production and addition of anti-IL-18 antibodies decreased both IL-4 and IL-5 production. Inhibition of IL-1beta and IL-18 secretion by DCs via inhibition of caspase-1 also led to a marked decrease of IL-4 and IL-5 by CD4(+) T cells. These results indicate that aluminum-containing adjuvants activate DCs and influence their ability to direct T(H)1 and T(H)2 responses through the secretion of IL-1beta and IL-18.

Aluminium hydroxide-induced granulomas in pigs

The effect of intramuscular injection of 40 mg/2 ml aluminium hydroxide in the neck of pigs was examined in a number of ways. The investigation followed repeated slaughterhouse reports, according to which 64.8% of pigs from one particular farm were found at slaughter to have one or more nodules in the muscles of the neck (group slaughtered). The pigs had been injected with a vaccine containing 40 mg/2 ml dose of aluminium hydroxide as adjuvant. Research consisted of two phases: first, an epidemiological study was carried out, aimed at determining the risk factors for the granulomas. The results indicated that the vaccine was to be held responsible for the formation of granulomas. A clinical trial was then performed to further substantiate the initial hypothesis, by comparing pigs, which were aseptically inoculated twice with either the original vaccine or the adjuvant alone (groups vaccine and adjuvant) to pigs inoculated twice with apyrogenic bi-distilled water (group water) and to pigs inoculated once with the adjuvant and once with apyrogenic bi-distilled water (group adjuvant/water). Both studies agreed in their conclusions, which indicate that the high amount of aluminium hydroxide was the cause of the granulomas.

Aluminium compounds for use in vaccines

Aluminium adjuvants are the most widely used adjuvants in both human and veterinary vaccines. These adjuvants have been used in practical vaccination for more than 60 years and are generally recognized as safe and as stimulators of Th2 immunity. The present review gives a short introduction to the pioneering research at the start of the use of aluminium compounds as adjuvants, including references on the chemistry of these compounds. Analytical methods for identifying the most commonly used aluminium compounds, such as boehmite and aluminium hydroxyphosphate, are mentioned. Emphasis is placed on the important factors for antigen adsorption and on the latest work using gene-deficient mice in the research of the mechanism of aluminium adjuvants in terms of cytokine and T-cell subset stimulation. Key references on the ability of aluminium adjuvants to stimulate IgE and also in vivo clearing of aluminium adjuvants are discussed. Furthermore, the review addresses the issue of local reactions in the context of injection route and local tissue disturbance. Possible new applications of aluminium adjuvants in, for example, combined aluminium-adsorbed protein and DNA oligonucleotide vaccines as well as the possible use of aluminium adjuvants in combination with IL-12 to stimulate Th1-type immune responses are mentioned.

Aluminium adjuvants—in retrospect and prospect

Aluminium compounds have been used as adjuvants in practical vaccination for more than 60 years to induce an early, an efficient and a long lasting protective immunity and are at present the most widely used adjuvants in both veterinary and human vaccines. Although the last two decades of systematic research into the nature of these adjuvants has contributed significantly to understanding their nature and their limitations as Th2 stimulators the more detailed mode of action of these adjuvants is still not completely understood. We have a comprehensive record of their behaviour and performance in practical vaccination, but an empirical approach to optimising their use in new vaccine formulations is still to some extent a necessity. The aim of the present review is to put the recent findings into a broader perspective to facilitate the application of these adjuvants in general and experimental vaccinology.

Evaluation of the bacterial endotoxin test for quantification of endotoxin contamination of porcine vaccines

We investigated the application of the bacterial endotoxin test for the quantification of the endotoxin contamination of various commercial porcine vaccines. In endotoxin-spiked samples, Freund's complete adjuvant and aluminum hydroxide gel adjuvant failed to interfere with the results of the endotoxin test, and both recovery ratios were within the permissible range mentioned in the Japanese Pharmacopoeia. At the various dilutions tested, none of the adjuvants in commercial porcine vaccines caused noteworthy interference in the test. In addition, none of the 39 samples of porcine vaccines approved in Japan induced an interfering effect in the endotoxin test. Our findings suggest that the bacterial endotoxin test using endotoxin-specific Limulus amoebocyte lysate (LAL) can detect endotoxin contamination in commercial porcine vaccines containing either oil or aluminum adjuvants.

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Effect of the degree of phosphate substitution in aluminum hydroxide adjuvant on the adsorption of phosphorylated proteins

Aluminum hydroxide adjuvant was pretreated with six concentrations of potassium dihydrogen phosphate to produce a series of adjuvants with various degrees of phosphate substitution for surface hydroxyl. The adsorption of three phosphorylated proteins (alpha casein, dephosphorylated alpha casein, and ovalbumin) by the phosphate-treated aluminum hydroxide adjuvants was studied. The phosphorylated proteins were adsorbed by ligand exchange of phosphate for hydroxyl even when an electrostatic repulsive force was present. However, the extent (adsorptive capacity) and strength (adsorptive coefficient) of adsorption was inversely related to the degree of phosphate substitution of the aluminum hydroxide adjuvant. Exposure of vaccines containing aluminum hydroxide adjuvant and phosphorylated antigens to phosphate ion in the formulation or during manufacture should be minimized to produce maximum adsorption of the antigen.

Microparticles as vaccine adjuvants and delivery systems

Adjuvants can be broadly divided into two groups, based on their principal mechanisms of action: vaccine delivery systems and immunostimulatory adjuvants. Vaccine delivery systems are generally particulate (e.g., emulsions, microparticles, immunostimulatory complexes and liposomes) and function mainly to target associated antigens into antigen-presenting cells. However, increasingly, more complex formulations are being developed in which delivery systems are exploited both for the delivery of antigens and also for the delivery of coadministered immunostimulatory adjuvants. The rationale for this approach is to ensure that both antigen and adjuvant are delivered into the same population of antigen-presenting cells. In addition, delivery systems can focus the effect of the adjuvants onto the key cells of the immune system and limit the systemic distribution of the adjuvant, to minimize its potential to induce adverse effects. The formulation and delivery of potent adjuvants in microparticles may allow the development of prophylactic and therapeutic vaccines against cancers and chronic infectious diseases, which are currently poorly controlled. In addition, microparticle formulations may also allow vaccines to be delivered mucosally.