Mechanism of immunopotentiation by aluminum-containing adjuvants elucidated by the relationship between antigen retention at the inoculation site and the immune response

Micronanoparticled risedronate exhibits potent vaccine adjuvant effects

Micro/Nano-scale particles are widely used as vaccine adjuvants to enhance immune response and improve antigen stability. While aluminum salt is one of the most common adjuvants approved for human use, its immunostimulatory capacity is suboptimal. In this study, we modified risedronate, an immunostimulant and anti-osteoporotic drug, to create zinc salt particle-based risedronate (Zn-RS), also termed particulate risedronate. Compared to soluble risedronate, micronanoparticled Zn-RS adjuvant demonstrated increased recruitment of innate cells, enhanced antigen uptake locally, and a similar antigen depot effect as aluminum salt. Furthermore, Zn-RS adjuvant directly and quickly stimulated immune cells, accelerated the formulation of germinal centers in lymph nodes, and facilitated the rapid production of antibodies. Importantly, Zn-RS adjuvant exhibited superior performance in both young and aged mice, effectively protecting against respiratory diseases such as SARS-CoV-2 challenge. Consequently, particulate risedronate showed great potential as an immune-enhancing vaccine adjuvant, particularly beneficial for vaccines targeting the susceptible elderly.

Head-to-Head Comparison of Novel Vaccine Technologies Comes with a Minefield of Challenges

Modern vaccine development is having a golden period, with a variety of novel subunit technologies being introduced into clinical development in recent years. This opens the opportunity to find the best platform to use for novel vaccine antigen candidates through head-to-head comparative studies. Seldom appreciated is, however, the fact that these different technologies often do not have the same optimal antigen dose ratio, prime-boost regime and peak timepoint for measuring immunity. Instead, the preclinical studies that make the basis for platform selection use standard protocols not optimized for individual vaccines and fail to make selection on an informed basis. Here, I discuss the opportunities we have to optimize vaccine platform technologies through a better understanding of vaccine priming kinetics, the optimal antigen dose and sampling time and location.

Formulation development and comparability studies with an aluminum-salt adjuvanted SARS-CoV-2 spike ferritin nanoparticle vaccine antigen produced from two different cell lines

The development of safe and effective second-generation COVID-19 vaccines to improve affordability and storage stability requirements remains a high priority to expand global coverage. In this report, we describe formulation development and comparability studies with a self-assembled SARS-CoV-2 spike ferritin nanoparticle vaccine antigen (called DCFHP), when produced in two different cell lines and formulated with an aluminum-salt adjuvant (Alhydrogel, AH). Varying levels of phosphate buffer altered the extent and strength of antigen-adjuvant interactions, and these formulations were evaluated for their (1) in vivo performance in mice and (2) in vitro stability profiles. Unadjuvanted DCFHP produced minimal immune responses while AH-adjuvanted formulations elicited greatly enhanced pseudovirus neutralization titers independent of ∼100%, ∼40% or ∼10% of the DCFHP antigen adsorbed to AH. These formulations differed, however, in their in vitro stability properties as determined by biophysical studies and a competitive ELISA for measuring ACE2 receptor binding of AH-bound antigen. Interestingly, after one month of 4°C storage, small increases in antigenicity with concomitant decreases in the ability to desorb the antigen from the AH were observed. Finally, we performed a comparability assessment of DCFHP antigen produced in Expi293 and CHO cells, which displayed expected differences in their N-linked oligosaccharide profiles. Despite consisting of different DCFHP glycoforms, these two preparations were highly similar in their key quality attributes including molecular size, structural integrity, conformational stability, binding to ACE2 receptor and mouse immunogenicity profiles. Taken together, these studies support future preclinical and clinical development of an AH-adjuvanted DCFHP vaccine candidate produced in CHO cells.

Periodic Mesoporous Organosilica as a Nanoadjuvant for Subunit Vaccines Elicits Potent Antigen-Specific Germinal Center Responses by Activating Naive B Cells

Infection diseases such as AIDS and COVID-19 remain challenging in regard to protective vaccine design, while adjuvants are critical for subunit vaccines to induce strong, broad, and durable immune responses against variable pathogens. Here, we demonstrate that periodic mesoporous organosilica (PMO) acts as a multifunctional nanoadjuvant by adsorbing recombinant protein antigens. It can effectively deliver antigens to lymph nodes (LNs), prolong antigen exposure, and rapidly elicit germinal center (GC) responses by directly activating naive B cells via the C-type lectin receptor signaling pathway. In mice, both the gp120 trimer (HIV-1 antigen) and the receptor-binding domain (SARS-CoV-2 antigen) with the PMO nanoadjuvant elicit potent and durable antibodies that neutralize heterologous virus strains. LN immune cells analysis shows that PMO helps to effectively activate the T-follicular helper cells, GC B cells, and memory B cells and eventually develop broad and durable humoral responses. Moreover, the PMO nanoadjuvant elicits a strong cellular immune response and shapes this immune response by eliciting high levels of effector T helper cell cytokines. This study identifies a promising nanoadjuvant for subunit vaccines against multiple pathogens.

Progress towards Adjuvant Development: Focus on Antiviral Therapy

In recent decades, vaccines have been extraordinary resources to prevent pathogen diffusion and cancer. Even if they can be formed by a single antigen, the addition of one or more adjuvants represents the key to enhance the response of the immune signal to the antigen, thus accelerating and increasing the duration and the potency of the protective effect. Their use is of particular importance for vulnerable populations, such as the elderly or immunocompromised people. Despite their importance, only in the last forty years has the search for novel adjuvants increased, with the discovery of novel classes of immune potentiators and immunomodulators. Due to the complexity of the cascades involved in immune signal activation, their mechanism of action remains poorly understood, even if significant discovery has been recently made thanks to recombinant technology and metabolomics. This review focuses on the classes of adjuvants under research, recent mechanism of action studies, as well as nanodelivery systems and novel classes of adjuvants that can be chemically manipulated to create novel small molecule adjuvants.

Formulation development and comparability studies with an aluminum-salt adjuvanted SARS-CoV-2 Spike ferritin nanoparticle vaccine antigen produced from two different cell lines

The development of safe and effective second-generation COVID-19 vaccines to improve affordability and storage stability requirements remains a high priority to expand global coverage. In this report, we describe formulation development and comparability studies with a self-assembled SARS-CoV-2 spike ferritin nanoparticle vaccine antigen (called DCFHP), when produced in two different cell lines and formulated with an aluminum-salt adjuvant (Alhydrogel, AH). Varying levels of phosphate buffer altered the extent and strength of antigen-adjuvant interactions, and these formulations were evaluated for their (1) in vivo performance in mice and (2) in vitro stability profiles. Unadjuvanted DCFHP produced minimal immune responses while AH-adjuvanted formulations elicited greatly enhanced pseudovirus neutralization titers independent of ∼100%, ∼40% or ∼10% of the DCFHP antigen adsorbed to AH. These formulations differed, however, in their in vitro stability properties as determined by biophysical studies and a competitive ELISA for measuring ACE2 receptor binding of AH-bound antigen. Interestingly, after one month of 4°C storage, small increases in antigenicity with concomitant decreases in the ability to desorb the antigen from the AH were observed. Finally, we performed a comparability assessment of DCFHP antigen produced in Expi293 and CHO cells, which displayed expected differences in their N-linked oligosaccharide profiles. Despite consisting of different DCFHP glycoforms, these two preparations were highly similar in their key quality attributes including molecular size, structural integrity, conformational stability, binding to ACE2 receptor and mouse immunogenicity profiles. Taken together, these studies support future preclinical and clinical development of an AH-adjuvanted DCFHP vaccine candidate produced in CHO cells.

Maturation of Aluminium Adsorbed Antigens Contributes to the Creation of Homogeneous Vaccine Formulations

Although aluminium-based vaccines have been used for almost over a century, their mechanism of action remains unclear. It is established that antigen adsorption to the adjuvant facilitates delivery of the antigen to immune cells at the injection site. To further increase our understanding of aluminium-based vaccines, it is important to gain additional insights on the interactions between the aluminium and antigens, including antigen distribution over the adjuvant particles. Immuno-assays can further help in this regard. In this paper, we evaluated how established formulation strategies (i.e., sequential, competitive, and separate antigen addition) applied to four different antigens and aluminium oxyhydroxide, lead to formulation changes over time. Results showed that all formulation samples were stable, and that no significant changes were observed in terms of physical-chemical properties. Antigen distribution across the bulk aluminium population, however, did show a maturation effect, with some initial dependence on the formulation approach and the antigen adsorption strength. Sequential and competitive approaches displayed similar results in terms of the homogeneity of antigen distribution across aluminium particles, while separately adsorbed antigens were initially more highly poly-dispersed. Nevertheless, the formulation sample prepared via separate adsorption also reached homogeneity according to each antigen adsorption strength. This study indicated that antigen distribution across aluminium particles is a dynamic feature that evolves over time, which is initially influenced by the formulation approach and the specific adsorption strength, but ultimately leads to homogeneous formulations.

Review: Unravelling the Role of DNA Sensing in Alum Adjuvant Activity

Public interest in vaccines is at an all-time high following the SARS-CoV-2 global pandemic. Currently, over 6 billion doses of various vaccines are administered globally each year. Most of these vaccines contain Aluminium-based adjuvants (alum), which have been known and used for almost 100 years to enhance vaccine immunogenicity. However, despite the historical use and importance of alum, we still do not have a complete understanding of how alum works to drive vaccine immunogenicity. In this article, we critically review studies investigating the mechanisms of action of alum adjuvants, highlighting some of the misconceptions and controversies within the area. Although we have emerged with a clearer understanding of how this ubiquitous adjuvant works, we have also highlighted some of the outstanding questions in the field. While these may seem mainly of academic interest, developing a more complete understanding of these mechanisms has the potential to rationally modify and improve the immune response generated by alum-adjuvanted vaccines.

Risk factors for granulomas in children following immunisation with aluminium adsorbed vaccines: A Danish population-based cohort study

BACKGROUND

Aluminium adsorbed vaccines may in some children cause severely itching nodules at the injection site, known as vaccination granulomas.

OBJECTIVE

To investigate vaccine-, child- and maternal level risk factors for the development of vaccination granulomas following immunisation with aluminium adsorbed vaccines.

METHODS

A Danish population-based cohort study with 553 932 children born in Denmark from 1 January 2009 to 31 December 2018, vaccinated with an aluminium adsorbed vaccine during the first year of life, followed until 31 December 2020. Poisson regression was used to estimate granuloma rate ratios according to type of adjuvant, accumulated dose of aluminium, timing of vaccination appointments, sex, gestational age, having siblings with granulomas, maternal age, and maternal ethnicity.

RESULTS

We identified 1 901 vaccination granuloma cases (absolute risk, 0.34%). Among vaccine level factors, revaccination (third vs first vaccination appointment, adjusted rate ratio [RR] 1.26, 95% confidence interval [CI] 1.03-1.55), the specific adjuvant used (aluminium phosphate vs hydroxide, RR 0.58, 95% CI 0.48-0.70) and dosage (≥1.0 mg vs <1.0 mg, RR 1.34, 95% CI 1.19-1.52) were associated with risk of granulomas; the timing of vaccination appointments was not. Among child level factors, female sex (vs males, RR 1.12, 95% CI, 1.02-1.22), prematurity (vs term birth, RR 0.71, 95% CI, 0.54-0.93) and having sibling(s) with granulomas (vs no siblings with granulomas, RR 46.15, 95% CI, 33.67-63.26) were associated with risk of granulomas. Among maternal level factors, non-Danish ethnicity (vs. Danish, RR 0.51, 95% CI, 0.42-0.63) and young maternal age (<20 yrs. vs 20-39 yrs., RR 0.46, 95% CI 0.25-0.83) were associated with risk of granulomas.

CONCLUSIONS

Several risk factors for vaccination granulomas at both the vaccine, child, and maternal level, was identified. Reducing the dose of aluminium or replacing aluminium hydroxide with aluminium phosphate could reduce the risk of granulomas. However, this must be balanced against the potential for reduced immunogenicity.

Nanoalum adjuvanted vaccines: small details make a big difference

Purified vaccine antigens offer important safety and reactogenicity advantages compared with live attenuated or whole killed virus and bacterial vaccines. However, they require the addition of adjuvants to induce the magnitude, duration and quality of immune response required to achieve protective immunity. Aluminium salts have been used as adjuvants in vaccines for almost a century. In the literature, they are often referred to as aluminium-based adjuvants (ABAs), or aluminium salt-containing adjuvants or more simply "alum". All these terms are used to group aluminium suspensions that are very different in terms of atomic composition, size, and shape. They differ also in stability, antigen-adsorption, and antigen-release kinetics. Critically, these parameters also have a profound effect on the character and magnitude of the immune response elicited. Recent findings suggest that, by reducing the size of aluminium from micro to nanometers, a more effective adjuvant is obtained, together with the ability to sterile filter the vaccine product. However, the behaviour of aluminium nanoparticles in vaccine formulations is different from microparticles, requiring specific formulation strategies, as well as a more detailed understanding of how formulation influences the immune response generated. Here we review the current state of art of aluminium nanoparticles as adjuvants, with a focus on their immunobiology, preparation methods, formulation optimisation and stabilisation.

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.

Targeting Lymph Node Niches Enhances Type 1 Immune Responses to Immunization

Generating robust CD4⁺ T-helper cell type 1 (Th1) responses is essential for protective vaccine-induced type 1 immunity. Here, we examine whether immunization formulation associated with enhanced vaccine efficacy promotes antigen targeting and cell recruitment into lymph node (LN) niches associated with optimal type 1 responses. Immunization with antigen and Toll-like receptor agonist emulsified in oil leads to an increased differentiation of IFNγ/TNF-α⁺ polyfunctional Th1 cells compared to an identical immunization in saline. Oil immunization results in a rapid delivery and persistence of antigen in interfollicular regions (IFRs) of the LN, whereas without oil, antigen is distributed in the medullary region. Following oil immunization, CXCL10-producing inflammatory monocytes accumulate in the IFR, which mobilizes antigen-specific CD4⁺ T cells into this niche. In this microenvironment, CD4⁺ T cells are advantageously positioned to encounter arriving IL-12-producing inflammatory dendritic cells (DCs). These data suggest that formulations delivering antigen to the LN IFR create an inflammatory niche that can improve vaccine efficacy.

Squalene-Based Influenza Vaccine Adjuvants and Their Impact on the Hemagglutinin-Specific B Cell Response

Influenza infections continue to cause significant annual morbidity and mortality despite ongoing influenza vaccine research. Adjuvants are administered in conjunction with influenza vaccines to enhance the immune response and strengthen protection against disease. Squalene-based emulsion adjuvants including MF59, AS03, and AF03, are registered for administration with influenza vaccines and are widely used in many countries. Squalene-based emulsion adjuvants induce a strong innate immune response, enhancing antigen presentation both quantitively and qualitatively to generate strong B cell responses and antibody production. They also diversify the reactivity profiles and strengthen the affinities of antibodies against the influenza hemagglutinin, increasing protection across virus clades. In this review, we consider the mechanisms of the enhancement of innate and adaptive immune responses by squalene-based emulsionSE adjuvants and the resulting increase in magnitude and breadth of hemagglutinin-specific B cell responses. We relate observed effects of SE adjuvants and current mechanistic understandings to events in responding lymph nodes. These insights will guide the rational design and optimization of influenza vaccines to provide broad and effective protection.

Vaccination against cocaine using a modifiable dendrimer nanoparticle platform

Pharmacological therapies for the treatment of cocaine addiction have had disappointing efficacy, and the lack of recent developments in the clinical care of cocaine-addicted patients indicates a need for novel treatment strategies. Recent studies have shown that vaccination against cocaine to elicit production of antibodies that reduce concentrations of free drug in the blood is a promising method to protect against the effects of cocaine and reduce rates of relapse. However, the poorly immunogenic nature of cocaine remains a major hurdle to active immunization. Therefore, we hypothesized that strategies to increase targeted exposure of cocaine to the immune system may produce a more effective vaccine. To specifically direct an immune response against cocaine, in the present study we have conjugated a cocaine analog to a dendrimer-based nanoparticle carrier with MHC II-binding moieties that previously has been shown to activate antigen-presenting cells necessary for antibody production. This strategy produced a rapid, prolonged, and high affinity anti-cocaine antibody response without the need for an adjuvant. Surprisingly, additional evaluation using multiple adjuvant formulations in two strains of inbred mice found adjuvants were either functionally redundant or deleterious in the vaccination against cocaine using this platform. The use of conditioned place preference in rats after administration of this vaccine provided proof of concept for the ability of this vaccine to diminish cocaine reward. Together these data demonstrate the intrinsic efficacy of an immune-targeting dendrimer-based cocaine vaccine, with a vast potential for design of future vaccines against other poorly immunogenic antigens by substitution of the conjugated cargo.

Vaccine Adjuvants Differentially Affect Kinetics of Antibody and Germinal Center Responses

Aluminum salts and squalene based oil-in-water emulsions (SE) are widely used adjuvants in licensed vaccines, yet their mechanisms are not fully known. Here we report that induction of antibody responses displays different kinetics dependent on the adjuvant used. SE facilitated a rapid antibody response in contrast to aluminum hydroxide (AH) and the depot-forming cationic liposome-based adjuvant (CAF01). Antigen given with the SE adjuvant rapidly reached follicular B cells in the draining lymph node, whereas antigen formulated in AH or CAF01 remained at the site of injection as a depot. Removal of the injection site early after immunization abrogated antibody responses only when antigen was given in the depot-forming adjuvants. Despite initial delays in B cell activation and germinal center (GC) formation when antigen was given in depot-forming adjuvants, the antibody levels reached higher magnitudes than when the antigen was formulated in SE. This study demonstrates that the kinetic aspect of antibody responses is critical in adjuvant benchmarking and suggests that the optimal vaccination regime depends on the adjuvant used.

Controlling timing and location in vaccines

Vaccines are one of the most powerful technologies supporting public health. The adaptive immune response induced by immunization arises following appropriate activation and differentiation of T and B cells in lymph nodes. Among many parameters impacting the resulting immune response, the presence of antigen and inflammatory cues for an appropriate temporal duration within the lymph nodes, and further within appropriate subcompartments of the lymph nodes– the right timing and location– play a critical role in shaping cellular and humoral immunity. Here we review recent advances in our understanding of how vaccine kinetics and biodistribution impact adaptive immunity, and the underlying immunological mechanisms that govern these responses. We discuss emerging approaches to engineer these properties for future vaccines, with a focus on subunit vaccines.

Engineered immunogen binding to alum adjuvant enhances humoral immunity

Adjuvants are central to the efficacy of subunit vaccines. Aluminum hydroxide (alum) is the most commonly used vaccine adjuvant, yet its adjuvanticity is often weak and mechanisms of triggering antibody responses remain poorly understood. We demonstrate that site-specific modification of immunogens with short peptides composed of repeating phosphoserine (pSer) residues enhances binding to alum and prolongs immunogen bioavailability. The pSer-modified immunogens formulated in alum elicited greatly increased germinal center, antibody, neutralizing antibody, memory and long-lived plasma cell responses compared to conventional alum-adsorbed immunogens. Mechanistically, pSer-immunogen:alum complexes form nanoparticles that traffic to lymph nodes and trigger B cell activation through multivalent and oriented antigen display. Direct uptake of antigen-decorated alum particles by B cells upregulated antigen processing and presentation pathways, further enhancing B cell activation. These data provide insights into mechanisms of action of alum and introduce a readily translatable approach to significantly improve humoral immunity to subunit vaccines using a clinical adjuvant.

Alum coupled to protein immunogens via site-specific phosphoserine-containing linkers enhances long-lived B cell responses and can selectively direct antibodies toward protective neutralizing epitopes.

The size of micro-crystalline tyrosine (MCT®) influences its recognition and uptake by THP-1 macrophages in vitro

The physicochemical hallmarks of particulate immunopotentiators play a pivotal role with regards to their adjuvanticity in vivo. These properties have not been fully characterised in the case of MCT®, an amino acid-based adjuvant used as an alternative to aluminium salts in subcutaneous allergy immunotherapy (SCIT). This study presents a full characterisation of MCT® and in a preliminary capacity reveals how parameters, specifically particle size, might influence the recognition of MCT® by antigen presenting cells (APCs) in vitro. Light microscopic analysis demonstrated that MCT® was composed of highly crystalline needles, the majority of which exceeded 10 μm in length under physiological conditions (median size – 20.8 μm). While the substantial length of crystals presented a significant barrier to cellular recognition and uptake, isolated incidences of perpendicular recognition were observed owing to the smaller comparative width of crystallites (median size – 2.8 μm). This appeared to allow a small proportion of material to be ingested both fully and partially by THP-1 macrophages, although further studies are required to unequivocally confirm this observation. Preferential recognition of needle tips also favoured the direct presentation of antigen to immune cells as proteinaceous adsorption appeared to be isolated to these regions. Furthermore, the data herein provide valuable insights into the mechanisms surrounding how this adjuvant potentiates an immunological response following administration.

The large size of MCT® crystallites partially stymies their recognition and uptake by THP-1 macrophages in vitro.

Slow Delivery Immunization Enhances HIV Neutralizing Antibody and Germinal Center Responses via Modulation of Immunodominance

Conventional immunization strategies will likely be insufficient for the development of a broadly neutralizing antibody (bnAb) vaccine for HIV or other difficult pathogens because of the immunological hurdles posed, including B cell immunodominance and germinal center (GC) quantity and quality. We found that two independent methods of slow delivery immunization of rhesus monkeys (RMs) resulted in more robust T follicular helper (TFH) cell responses and GC B cells with improved Env-binding, tracked by longitudinal fine needle aspirates. Improved GCs correlated with the development of >20-fold higher titers of autologous nAbs. Using a new RM genomic immunoglobulin locus reference, we identified differential IgV gene use between immunization modalities. Ab mapping demonstrated targeting of immunodominant non-neutralizing epitopes by conventional bolus-immunized animals, whereas slow delivery-immunized animals targeted a more diverse set of epitopes. Thus, alternative immunization strategies can enhance nAb development by altering GCs and modulating the immunodominance of non-neutralizing epitopes.

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.

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.

Enhancing Efficacy and Stability of an Antiheroin Vaccine: Examination of Antinociception, Opioid Binding Profile, and Lethality

In recent years, drug conjugate vaccines have shown promise as therapeutics for substance use disorder. As a means to improve the efficacy of a heroin conjugate vaccine, we systematically explored 20 vaccine formulations with varying combinations of carrier proteins and adjuvants. In regard to adjuvants, we explored a Toll-like receptor 9 (TLR9) agonist and a TLR3 agonist in the presence of alum. The TLR9 agonist was cytosine-guanine oligodeoxynucleotide 1826 (CpG ODN 1826), while the TLR3 agonist was virus-derived genomic doubled-stranded RNA (dsRNA). The vaccine formulations containing TLR3 or TLR9 agonist alone elicited strong antiheroin antibody titers and blockade of heroin-induced antinociception when formulated with alum; however, a combination of TLR3 and TLR9 adjuvants did not result in improved efficacy. Investigation of month-long stability of the two lead formulations revealed that the TLR9 but not the TLR3 formulation was stable when stored as a lyophilized solid or as a liquid over 30 days. Furthermore, mice immunized with the TLR9 + alum heroin vaccine gained significant protection from lethal heroin doses, suggesting that this vaccine formulation is suitable for mitigating the harmful effects of heroin, even following month-long storage at room temperature.

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.

Conjugate Vaccine Immunotherapy for Substance Use Disorder

Substance use disorder, especially in relation to opioids such as heroin and fentanyl, is a significant public health issue and has intensified in recent years. As a result, substantial interest exists in developing therapeutics to counteract the effects of abused drugs. A promising universal strategy for antagonizing the pharmacology of virtually any drug involves the development of a conjugate vaccine, wherein a hapten structurally similar to the target drug is conjugated to an immunogenic carrier protein. When formulated with adjuvants and immunized, the immunoconjugate should elicit serum IgG antibodies with the ability to sequester the target drug to prevent its entry to the brain, thereby acting as an immunoantagonist. Despite the failures of first-generation conjugate vaccines against cocaine and nicotine in clinical trials, second-generation vaccines have shown dramatically improved performance in preclinical models, thus renewing the potential clinical utility of conjugate vaccines in curbing substance use disorder. This review explores the critical design elements of drug conjugate vaccines such as hapten structure, adjuvant formulation, bioconjugate chemistry, and carrier protein selection. Methods for evaluating these vaccines are discussed, and recent progress in vaccine development for each drug is summarized.

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.

Alpha-D-glucan nanoparticulate adjuvant induces a transient inflammatory response at the injection site and targets antigen to migratory dendritic cells

Biodegradable nanoparticles with functionalized surfaces are attractive candidates as vaccine adjuvants. Nano-11 are cationic dendrimer-like α-D-glucan nanoparticles with a diameter of 70–80 nm. Mice injected with antigen formulated with Nano-11 developed antibody titers that were similar or greater than antigen with aluminum adjuvant. Utilizing an in vivo imaging system, Nano-11 was shown to remain at the injection site after administration and cleared gradually over the course of 3 weeks. Injection of Nano-11 induced a transient inflammatory response characterized by recruitment of a mixed population of inflammatory cells, predominantly monocytes and macrophages with relatively few neutrophils. Recruited Mac-2⁺macrophages efficiently phagocytized the majority of Nano-11 at the injection site. Fluorescently labeled Nano-11 was present in cells in the draining lymph nodes 1 day after injection, with the majority contained in migratory dendritic cells. Injection of ovalbumin adsorbed to Nano-11 resulted in an increase of ovalbumin-containing cells in draining lymph nodes. Nano-11 delivered more antigen to antigen-presenting cells on a per cell basis and demonstrated more specific targeting to highly immunopotentiating migratory dendritic cells compared with soluble or aluminum hydroxide adsorbed ovalbumin. These results support the efficacy of Nano-11 and its potential use as a next generation vaccine adjuvant.

A plant-derived nanoparticle boosts the immune system’s response to foreign stimuli, such as vaccines, through newly discovered mechanisms. Harm HogenEsch and his team from Purdue University, USA, previously discovered that their formulated nanoparticle adjuvant, Nano-11, increased immune responses to stimuli in mice. Adjuvants are formulations often co-administered with vaccines to promote interaction with the host’s immune system, conferring greater protection. In this study, the scientists found that Nano-11 functions by inducing a temporary inflammation, attracting immune cells to the injection site. The nanoparticles also facilitate the transport of the stimuli to the lymph nodes. Nano-11 is metabolized without deposition in any major internal organs, suggesting a positive safety profile. As current aluminum-based adjuvants are sometimes poorly effective and can cause local adverse reactions, nanoparticle-based potentiators such as Nano-11 may form the next generation of adjuvants.

Dynamics of APC recruitment at the site of injection following injection of vaccine adjuvants

Vaccines often contain adjuvants to strengthen the response to the vaccine antigen. However, their modes of action at the site of injection (SOI) are poorly understood. Therefore, we assessed the local effects of adjuvant on the innate immune system in mice. We investigated the safe, widely used adjuvants MF59 and aluminum hydroxide (alum), as well as trehalose-6,6'-dibehenate (TDB), Complete Freund's Adjuvant (CFA) and the Toll-Like-Receptor-ligands lipopolysaccharide (LPS) and Pam3CysSerLys4 (Pam₃CSK₄). We assessed muscle immune cell infiltration after adjuvant injection and observed 16h post immunization (hpi) an increased influx with CFA, MF59 and TDB, but not with alum, LPS or Pam₃CSK₄. An elevated influx with the latter three became visible only 72hpi. Contribution of granulocytes, macrophages and dendritic cells to the influx differed per adjuvant and in time. Adjuvants generally induced a local pro-inflammatory micro-milieu that was transient except for CFA and TDB. The gene expression of CXCL-1, CCL-2 and CCL-5, involved in recruitment of immune cells, varied per adjuvant and corresponded grossly with the observed influx of granulocytes and monocytes/macrophages. Muscles injected with CFA or MF59 (when co-injected with peptide) resulted in APC ex vivo capable to induce proliferation of peptide-specific T-cells. By adding in vitro an excess of peptide to the APC/T cell co-cultures, we observed an adjuvant-enhanced co-stimulation or antigen presentation by APC after CFA- but not MF59-injection. After TDB-injection this effect was observed only at 72hpi, but not 24hpi. Thus the cellular influx profile and the local cytokine and chemokine micro-milieu in the muscle were strongly influenced by the type of adjuvant. Additionally, the capacity of muscle APC to load and present antigen was affected by the adjuvant. These findings may assist the development of novel adjuvanted vaccines in a more rational manner.

Controlled release of antigen and Toll-like receptor ligands from PLGA nanoparticles enhances immunogenicity

AIM

Dendritic cells rapidly capture nanoparticles and induce a potent cellular immune response. It is yet unknown whether the immunological response induced by slow release of encapsulated versus soluble antigen and adjuvant is superior.

MATERIALS & METHODS

The kinetics of poly(lactic-co-glycolic acid) PLGA nanoparticles antigen release was studied by the DQ-bovine serum albumin (BSA) self-quenching antigen model. The immunological response induced was evaluated by means of dendritic cell activation/maturation markers, cytokine production and their ability to drive antigen-specific T-cell proliferation.

RESULTS & CONCLUSION

PLGA-encapsulated antigen and adjuvant showed an enhanced T-cell response when compared with soluble vaccine components by increasing antigenicity and adjuvanticity. Although the kinetic profile followed the same pattern, encapsulation increased strength and duration of the response.

From Stock Bottle to Vaccine: Elucidating the Particle Size Distributions of Aluminum Adjuvants Using Dynamic Light Scattering

The physicochemical properties of aluminum salts are key determinants of their resultant adjuvanticity in vivo when administered as part of a vaccine. While there are links between particle size and the efficacy of the immune response, the limited literature directly characterizing the PSD of aluminum adjuvants has stymied the elucidation of such a relationship for these materials. Hence, this comparative study was undertaken to monitor the PSD of aluminum adjuvants throughout the process of vaccine formulation using DLS. A significant proportion of the stock suspensions was highly agglomerated (>9 μm) and Alhydrogel® exhibited the smallest median size (2677 ± 120 nm) in comparison to Adju-Phos® or Imject alum® (7152 ± 308 and 7294 ± 146 nm respectively) despite its large polydispersity index (PDI). Dilution of these materials induced some degree of disaggregation within all samples with Adju-Phos® being the most significantly affected. The presence of BSA caused the median size of Alhydrogel® to increase but these trends were not evident when model vaccines were formulated with either Adju-Phos® or Imject alum®. Nevertheless, Alhydrogel® and Adju-Phos® exhibited comparable median sizes in the presence of this protein (4194 ± 466 and 4850 ± 501 nm respectively) with Imject alum® being considerably smaller (2155 ± 485 nm). These results suggest that the PSD of aluminum adjuvants is greatly influenced by dilution and the degree of protein adsorption experienced within the vaccine itself. The size of the resultant antigen-adjuvant complex may be important for its immunological recognition and subsequent clearance from the injection site.

Overview of Vaccine Adjuvants: Introduction, History, and Current Status

Adjuvants are included in sub-unit or recombinant vaccines to enhance the potency of poorly immunogenic antigens. Adjuvant discovery is as complex as it is a multidiscplinary intersection of formulation science, immunology, toxicology, and biology. Adjuvants such as alum, which have been in use for the past 90 years, have illustrated that adjuvant research is a methodical process. As science advances, new analytical tools are developed which allows us to delve deeper into the various mechanisms that generates a potent immune response. Additionally, these new techniques help the field learn about our existing vaccines and what makes them safe, and effective, allowing us to leverage that in the next generation of vaccines. Our goal in this chapter is to define the concept, need, and mechanism of adjuvants in the vaccine field while describing its history, present use, and future prospects. More details on individual adjuvants and their formulation, development, mechanism, and use will be covered in depth in the next chapters.

Co-Administration of Lipid Nanoparticles and Sub-Unit Vaccine Antigens Is Required for Increase in Antigen-Specific Immune Responses in Mice

A vast body of evidence suggests that nanoparticles function as potent immune-modulatory agents. We have previously shown that Merck proprietary Lipid NanoParticles (LNPs) markedly boost B-cell and T-cell responses to sub-unit vaccine antigens in mice. To further evaluate the specifics of vaccine delivery and dosing regimens in vivo, we performed immunogenicity studies in BALB/c and C57BL/6 mice using two model antigens, Hepatitis B Surface Antigen (HBsAg) and Ovalbumin (OVA), respectively. To assess the requirement for co-administration of antigen and LNP for the elicitation of immune responses, we evaluated immune responses after administering antigen and LNP to separate limbs, or administering antigen and LNP to the same limb but separated by 24 h. We also evaluated formulations combining antigen, LNP, and aluminum-based adjuvant amorphous aluminum hydroxylphosphate sulfate (MAA) to look for synergistic adjuvant effects. Analyses of antigen-specific B-cell and T-cell responses from immunized mice revealed that the LNPs and antigens must be co-administered—both at the same time and in the same location—in order to boost antigen-specific immune responses. Mixing of antigen with MAA prior to formulation with LNP did not impact the generation of antigen-specific B-cell responses, but drastically reduced the ability of LNPs to boost antigen-specific T-cell responses. Overall, our data demonstrate that the administration of LNPs and vaccine antigen together enables their immune-stimulatory properties.

A nanoparticle-based nicotine vaccine and the influence of particle size on its immunogenicity and efficacy

Traditional hapten-protein conjugate nicotine vaccines have shown less than desired immunological efficacy due to their poor recognition and internalization by immune cells. We developed a novel lipid-polymeric hybrid nanoparticle-based nicotine vaccine to enhance the immunogenicity of the conjugate vaccine, and studied the influence of particle size on its immunogenicity and pharmacokinetic efficacy. The results demonstrated that the nanovaccines, regardless of size, could induce a significantly stronger immune response against nicotine compared to the conjugate vaccine. Particularly, a significantly higher anti-nicotine antibody titer was achieved by the 100 compared to the 500nm nanovaccine. In addition, both the 100 and 500nm nanovaccines reduced the distribution of nicotine into the brain significantly. The 100nm nanovaccine exhibited better pharmacokinetic efficacy than the 500nm nanovaccine in the presence of alum adjuvant. These results suggest that a lipid-polymeric nanoparticle-based nicotine vaccine is a promising candidate to treat nicotine dependence.

Aluminum adjuvants of vaccines injected into the muscle: Normal fate, pathology and associated disease

Aluminum oxyhydroxide (Alhydrogel(®)) is a nano-crystalline compound forming aggregates that has been introduced in vaccine for its immunologic adjuvant effect in 1926. It is the most commonly used adjuvant in human and veterinary vaccines but mechanisms by which it stimulates immune responses remain ill-defined. Although generally well tolerated on the short term, it has been suspected to occasionally cause delayed neurologic problems in susceptible individuals. In particular, the long-term persistence of aluminic granuloma also termed macrophagic myofasciitis is associated with chronic arthromyalgias and fatigue and cognitive dysfunction. Safety concerns largely depend on the long biopersistence time inherent to this adjuvant, which may be related to its quick withdrawal from the interstitial fluid by avid cellular uptake; and the capacity of adjuvant particles to migrate and slowly accumulate in lymphoid organs and the brain, a phenomenon documented in animal models and resulting from MCP1/CCL2-dependant translocation of adjuvant-loaded monocyte-lineage cells (Trojan horse phenomenon). These novel insights strongly suggest that serious re-evaluation of long-term aluminum adjuvant phamacokinetics and safety should be carried out.

Beyond antigens and adjuvants: formulating future vaccines

The need to optimize vaccine potency while minimizing toxicity in healthy recipients has motivated studies of the formulation of vaccines to control how, when, and where antigens and adjuvants encounter immune cells and other cells/tissues following administration. An effective subunit vaccine must traffic to lymph nodes (LNs), activate both the innate and adaptive arms of the immune system, and persist for a sufficient time to promote a mature immune response. Here, we review approaches to tailor these three aspects of vaccine function through optimized formulations. Traditional vaccine adjuvants activate innate immune cells, promote cell-mediated transport of antigen to lymphoid tissues, and promote antigen retention in LNs. Recent studies using nanoparticles and other lymphatic-targeting strategies suggest that direct targeting of antigens and adjuvant compounds to LNs can also enhance vaccine potency without sacrificing safety. The use of formulations to regulate biodistribution and promote antigen and inflammatory cue co-uptake in immune cells may be important for next-generation molecular adjuvants. Finally, strategies to program vaccine kinetics through novel formulation and delivery strategies provide another means to enhance immune responses independent of the choice of adjuvant. These technologies offer the prospect of enhanced efficacy while maintaining high safety profiles necessary for successful vaccines.

Patterns of binding of aluminum-containing adjuvants to Haemophilus influenzae type b and meningococcal group C conjugate vaccines and components

The basis of Haemophilus influenzae type b (Hib) and Neisseria meningitidis serogroup C (MenC) glycoconjugates binding to aluminum-containing adjuvants was studied. By measuring the amount of polysaccharide and protein in the non-adsorbed supernatant, the adjuvant, aluminum phosphate, AlPO4, was found to be less efficient than aluminum hydroxide, Al(OH)3 at binding to the conjugates, at concentrations relevant to licensed vaccine formulations and when equimolar. At neutral pH, binding of TT conjugates to AlPO4 was facilitated through the carrier protein, with only weak binding of AlPO4 to CRM197 being observed. There was slightly higher binding of either adjuvant to tetanus toxoid conjugates, than to CRM197 conjugates. This was verified in AlPO4 formulations containing DTwP-Hib, where the adsorption of TT-conjugated Hib was higher than CRM197-conjugated Hib. At neutral pH, the anionic Hib and MenC polysaccharides did not appreciably bind to AlPO4, but did bind to Al(OH)3, due to electrostatic interactions. Phosphate ions reduced the binding of the conjugates to the adjuvants. These patterns of adjuvant adsorption can form the basis for future formulation studies with individual and combination vaccines containing saccharide-protein conjugates.

Antibodies elicited by yeast glycoproteins recognize HIV-1 virions and potently neutralize virions with high mannose N-glycans

The glycan shield on the human immunodeficiency virus 1 (HIV-1) envelope (Env) glycoprotein has drawn attention as a target for HIV-1 vaccine design given that an increasing number of potent and broadly neutralizing antibodies (bNAbs) recognize epitopes entirely or partially comprised of high mannose type N-linked glycans. In an attempt to generate immunogens that target the glycan shield of HIV-1, we previously engineered a triple mutant (TM) strain of Saccharomyces cerevisiae that results in exclusive presentation of high mannose type N-glycans, and identified five TM yeast glycoproteins that support strong binding of 2G12, a bNAb that targets a cluster of high mannose glycans on the gp120 subunit of Env. Here, we further analyzed the antigenicity and immunogenicity of these proteins in inducing anti-HIV responses. Our study demonstrated that the 2G12-reactive TM yeast glycoproteins efficiently bound to recently identified bNAbs including PGT125-130 and PGT135 that recognize high mannose glycan-dependent epitopes. Immunization of rabbits with a single TM yeast glycoprotein (Gp38 or Pst1), when conjugated to a promiscuous T-cell epitope peptide and coadministered with a Toll-like receptor 2 agonist, induced glycan-specific HIV-1 Env cross-reactive antibodies. The immune sera bound to both synthetic mannose oligosaccharides and gp120 proteins from a broad range of HIV-1 strains. The purified antibodies recognized and captured virions that contain both complex- and high mannose-type of N-glycans, and potently neutralized virions from different HIV-1 clades but only when the virions were enforced to retain high mannose N-glycans. This study provides insights into the elicitation of anti-carbohydrate, HIV-1 Env-cross reactive antibodies with a heterologous glycoprotein and may have applications in the design and administration of immunogens that target the viral glycan shield for development of an effective HIV-1 vaccine.

The avian influenza vaccine Emerflu. Why did it fail?

Emerflu is an inactivated, split-virion pandemic preparedness vaccine, containing 30 μg of hemagglutinin (HA) and 600 μg of aluminum hydroxide adjuvant. It is administered in two doses, 3 weeks apart. Only moderate immunogenicity was evident from clinical studies with the vaccine in adults, and HA antibody responses were below the criteria established by the EMA and US FDA for licensure. With the exception of Australia, the vaccine remains unlicensed. Further clinical development appears to have been suspended, and newer adjuvants such as MF59 and AS03 have since demonstrated safety and superior immunogenicity with lower HA doses. Emerflu is symbolic of the failure of aluminum salts as an adjuvant for influenza vaccines. Reasons for this failure are unclear, and may reflect problems with the adjuvant-antigen complex or interference in the immune response by heterosubtypic immunity.

The mechanisms of action of vaccines containing aluminum adjuvants: an in vitro vs in vivo paradigm

Adjuvants such as the aluminum compounds (alum) have been dominantly used in many vaccines due to their immunopotentiation and safety records since 1920s. However, how these mineral agents influence the immune response to vaccination remains elusive. Many hypotheses exist as to the mode of action of these adjuvants, such as depot formation, antigen (Ag) targeting, and the induction of inflammation. These hypotheses are based on many in vitro and few in vivo studies. Understanding how cells interact with adjuvants in vivo will be crucial to fully understanding the mechanisms of action of these adjuvants. Interestingly, how alum influences the target cell at both the cellular and molecular level, and the consequent innate and adaptive responses, will be critical in the rational design of effective vaccines against many diseases. Thus, in this review, mechanisms of action of alum have been discussed based on available in vitro vs in vivo evidences to date.

Systematic review of potential health risks posed by pharmaceutical, occupational and consumer exposures to metallic and nanoscale aluminum, aluminum oxides, aluminum hydroxide and its soluble salts

Abstract Aluminum (Al) is a ubiquitous substance encountered both naturally (as the third most abundant element) and intentionally (used in water, foods, pharmaceuticals, and vaccines); it is also present in ambient and occupational airborne particulates. Existing data underscore the importance of Al physical and chemical forms in relation to its uptake, accumulation, and systemic bioavailability. The present review represents a systematic examination of the peer-reviewed literature on the adverse health effects of Al materials published since a previous critical evaluation compiled by Krewski et al. (2007) . Challenges encountered in carrying out the present review reflected the experimental use of different physical and chemical Al forms, different routes of administration, and different target organs in relation to the magnitude, frequency, and duration of exposure. Wide variations in diet can result in Al intakes that are often higher than the World Health Organization provisional tolerable weekly intake (PTWI), which is based on studies with Al citrate. Comparing daily dietary Al exposures on the basis of "total Al"assumes that gastrointestinal bioavailability for all dietary Al forms is equivalent to that for Al citrate, an approach that requires validation. Current occupational exposure limits (OELs) for identical Al substances vary as much as 15-fold. The toxicity of different Al forms depends in large measure on their physical behavior and relative solubility in water. The toxicity of soluble Al forms depends upon the delivered dose of Al(+3) to target tissues. Trivalent Al reacts with water to produce bidentate superoxide coordination spheres [Al(O2)(H2O4)(+2) and Al(H2O)6 (+3)] that after complexation with O2(•-), generate Al superoxides [Al(O2(•))](H2O5)](+2). Semireduced AlO2(•) radicals deplete mitochondrial Fe and promote generation of H2O2, O2 (•-) and OH(•). Thus, it is the Al(+3)-induced formation of oxygen radicals that accounts for the oxidative damage that leads to intrinsic apoptosis. In contrast, the toxicity of the insoluble Al oxides depends primarily on their behavior as particulates. Aluminum has been held responsible for human morbidity and mortality, but there is no consistent and convincing evidence to associate the Al found in food and drinking water at the doses and chemical forms presently consumed by people living in North America and Western Europe with increased risk for Alzheimer's disease (AD). Neither is there clear evidence to show use of Al-containing underarm antiperspirants or cosmetics increases the risk of AD or breast cancer. Metallic Al, its oxides, and common Al salts have not been shown to be either genotoxic or carcinogenic. Aluminum exposures during neonatal and pediatric parenteral nutrition (PN) can impair bone mineralization and delay neurological development. Adverse effects to vaccines with Al adjuvants have occurred; however, recent controlled trials found that the immunologic response to certain vaccines with Al adjuvants was no greater, and in some cases less than, that after identical vaccination without Al adjuvants. The scientific literature on the adverse health effects of Al is extensive. Health risk assessments for Al must take into account individual co-factors (e.g., age, renal function, diet, gastric pH). Conclusions from the current review point to the need for refinement of the PTWI, reduction of Al contamination in PN solutions, justification for routine addition of Al to vaccines, and harmonization of OELs for Al substances.

Working together: interactions between vaccine antigens and adjuvants

The development of vaccines containing adjuvants has the potential to enhance antibody and cellular immune responses, broaden protective immunity against heterogeneous pathogen strains, enable antigen dose sparing, and facilitate efficacy in immunocompromised populations. Nevertheless, the structural interplay between antigen and adjuvant components is often not taken into account in the published literature. Interactions between antigen and adjuvant formulations should be well characterized to enable optimum vaccine stability and efficacy. This review focuses on the importance of characterizing antigen-adjuvant interactions by summarizing findings involving widely used adjuvant formulation platforms, such as aluminum salts, emulsions, lipid vesicles, and polymer-based particles. Emphasis is placed on the physicochemical basis of antigen-adjuvant associations and the appropriate analytical tools for their characterization, as well as discussing the effects of these interactions on vaccine potency.

Injection route and TLR9 agonist addition significantly impact heroin vaccine efficacy

Active immunization is an effective means of blocking the pharmacodynamic effects of drugs and holds promise as a treatment for heroin addiction. Previously, we demonstrated the efficacy of our first-generation vaccine in blocking heroin self-administration in rats, however, many vaccine components can be modified to further improve performance. Herein we examine the effects of varying heroin vaccine injection route and adjuvant formulation. Mice immunized via subcutaneous (sc) injection exhibited inferior anti-heroin titers compared to intraperitoneal (ip) and sc/ip coadministration injection routes. Addition of TLR9 agonist cytosine-guanine oligodeoxynucleotide 1826 (CpG ODN 1826) to the original alum adjuvant elicited superior antibody titers and opioid affinities compared to alum alone. To thoroughly assess vaccine efficacy, full dose–response curves were generated for heroin-induced analgesia in both hot plate and tail immersion tests. Mice treated with CpG ODN 1826 exhibited greatly shifted dose–response curves (10–13-fold vs unvaccinated controls) while non-CpG ODN vaccine groups did not exhibit the same robust effect (2–7-fold shift for ip and combo, 2–3-fold shift for sc). Our results suggest that CpG ODN 1826 is a highly potent adjuvant, and injection routes should be considered for development of small molecule–protein conjugate vaccines. Lastly, this study has established a new standard for assessing drugs of abuse vaccines, wherein a full dose–response curve should be performed in an appropriate behavioral task.

Increasing the potency of an alhydrogel-formulated anthrax vaccine by minimizing antigen-adjuvant interactions

Aluminum salts are the most widely used vaccine adjuvants, and phosphate is known to modulate antigen-adjuvant interactions. Here we report an unexpected role for phosphate buffer in an anthrax vaccine (SparVax) containing recombinant protective antigen (rPA) and aluminum oxyhydroxide (AlOH) adjuvant (Alhydrogel). Phosphate ions bind to AlOH to produce an aluminum phosphate surface with a reduced rPA adsorption coefficient and binding capacity. However, these effects continued to increase as the free phosphate concentration increased, and the binding of rPA changed from endothermic to exothermic. Crucially, phosphate restored the thermostability of bound rPA so that it resembled the soluble form, even though it remained tightly bound to the surface. Batches of vaccine with either 0.25 mM (subsaturated) or 4 mM (saturated) phosphate were tested in a disease model at batch release, which showed that the latter was significantly more potent. Both formulations retained their potency for 3 years. The strongest aluminum adjuvant effects are thus likely to be via weakly attached or easily released native-state antigen proteins.