The controversial relationship between NLRP3, alum, danger signals and the next-generation adjuvants

Co-formulation of the rF1V plague vaccine with depot-formulated cytokines enhances immunogenicity and efficacy to elicit protective responses against aerosol challenge in mice

This study evaluated a depot-formulated cytokine-based adjuvant to improve the efficacy of the recombinant F1V (rF1V) plague vaccine and examined the protective response following aerosol challenge in a murine model. The results of this study showed that co-formulation of the Alhydrogel-adsorbed rF1V plague fusion vaccine with the depot-formulated cytokines recombinant human interleukin 2 (rhuIL-2) and/or recombinant murine granulocyte macrophage colony-stimulating factor (rmGM-CSF) significantly enhances immunogenicity and significant protection at lower antigen doses against a lethal aerosol challenge. These results provide additional support for the co-application of the depot-formulated IL-2 and/or GM-CSF cytokines to enhance vaccine efficacy.

Novel adjuvants in allergen-specific immunotherapy: where do we stand?

Type I hypersensitivity, or so-called type I allergy, is caused by Th2-mediated immune responses directed against otherwise harmless environmental antigens. Currently, allergen-specific immunotherapy (AIT) is the only disease-modifying treatment with the potential to re-establish clinical tolerance towards the corresponding allergen(s). However, conventional AIT has certain drawbacks, including long treatment durations, the risk of inducing allergic side effects, and the fact that allergens by themselves have a rather low immunogenicity. To improve AIT, adjuvants can be a powerful tool not only to increase the immunogenicity of co-applied allergens but also to induce the desired immune activation, such as promoting allergen-specific Th1- or regulatory responses. This review summarizes the knowledge on adjuvants currently approved for use in human AIT: aluminum hydroxide, calcium phosphate, microcrystalline tyrosine, and MPLA, as well as novel adjuvants that have been studied in recent years: oil-in-water emulsions, virus-like particles, viral components, carbohydrate-based adjuvants (QS-21, glucans, and mannan) and TLR-ligands (flagellin and CpG-ODN). The investigated adjuvants show distinct properties, such as prolonging allergen release at the injection site, inducing allergen-specific IgG production while also reducing IgE levels, as well as promoting differentiation and activation of different immune cells. In the future, better understanding of the immunological mechanisms underlying the effects of these adjuvants in clinical settings may help us to improve AIT.

Vaccines and Dementia: Part I. Non-Specific Immune Boosting with BCG: History, Ligands, and Receptors

Vaccines such as Bacille Calmette-Guérin (BCG) can apparently defer dementia onset with an efficacy better than all drugs known to date, as initially reported by Gofrit et al. (PLoS One14, e0224433), now confirmed by other studies. Understanding how and why is of immense importance because it could represent a sea-change in how we manage patients with mild cognitive impairment through to dementia. Given that infection and/or inflammation are likely to contribute to the development of dementias such as Alzheimer's disease (Part II of this work), we provide a historical and molecular background to how vaccines, adjuvants, and their component molecules can elicit broad-spectrum protective effects against diverse agents. We review early studies in which poxvirus, herpes virus, and tuberculosis (TB) infections afford cross-protection against unrelated pathogens, a concept known as 'trained immunity'. We then focus on the attenuated TB vaccine, BCG, that was introduced to protect against the causative agent of TB, Mycobacterium tuberculosis. We trace the development of BCG in the 1920 s through to the discovery, by Freund and McDermott in the 1940 s, that extracts of mycobacteria can themselves exert potent immunostimulating (adjuvant) activity; Freund's complete adjuvant based on mycobacteria remains the most potent immunopotentiator reported to date. We then discuss whether the beneficial effects of BCG require long-term persistence of live bacteria, before focusing on the specific mycobacterial molecules, notably muramyl dipeptides, that mediate immunopotentiation, as well as the receptors involved. Part II addresses evidence that immunopotentiation by BCG and other vaccines can protect against dementia development.

NLRP3 inflammasome-mediated pyroptosis involvement in cadmium exposure-induced cognitive deficits via the Sirt3-mtROS axis

Cadmium (Cd), a toxic heavy metal, exerts deleterious effects on neuronal survival and cognitive function. NOD-like receptor 3 (NLRP3) inflammasome-dependent pyroptosis has been linked to Cd-induced cytotoxicity. The current research intended to elucidate the role of NLRP3 inflammasome-mediated pyroptosis in Cd-evoked neuronal death and cognitive impairments and the underlying mechanisms. Exposure to 1 mg/kg Cd for 8 weeks led to hippocampal-dependent cognitive deficits and neural/synaptic damage in mice. NLRP3 inflammasome-related protein expression (NLRP3, ASC, and caspase1 p20) and neuronal pyroptosis were significantly upregulated in Cd-treated hippocampi and SH-SY5Y cells. Moreover, pretreatment with the NLRP3 inhibitor MCC950 mitigated Cd-elicited NLRP3 inflammasome activation and subsequent neuronal pyroptosis in SH-SY5Y cells. Furthermore, exposure to Cd downregulated Sirt3 expression, suppressed SOD2 activity by hyperacetylation, and enhanced mtROS accumulation in vivo and in vitro. Notably, Cd-induced NLRP3 inflammasome-dependent neuronal pyroptosis was attenuated by a mtROS scavenger or Sirt3 overexpression in SH-SY5Y cells. In addition, Cd failed to further suppress SOD activity and activate NLRP3 inflammasome-dependent neuronal pyroptosis in Sirt3 shRNA-treated SH-SY5Y cells. Collectively, our findings indicate that Cd exposure induces neuronal injury and cognitive deficits by activating NLRP3 inflammasome-dependent neuronal pyroptosis and that activation of the NLRP3 inflammasome is partially mediated by the Sirt3-mtROS axis.

Size matters in non-canonical inflammasome activation and cell-mediated immunity

Particulate adjuvants are key components of many approved vaccines, but their mechanism of adjuvanticity is debated. Muñoz-Wolf et al.1 find that 50-nm particles maximize cell-mediated immune responses by activating the caspase-11 inflammasome, providing mechanistic insight to particulate adjuvant technologies.

Lycium barbarum polysaccharides-loaded Particulate Alum via Pickering emulsion as an adjuvant to enhance immune responses

Pickering emulsion has great potential as a vaccine adjuvant due to its unique advantages such as its high antigen loading efficiency, great stability, etc. Among several adjuvants on the market, aluminum adjuvant (Alum) is the most widely used at present. However, problems such as the inability to effectively induce cellular immunity and the poor effect on subunit vaccines limit the application of Alum. As an immunopotentiator, Lycium barbarum polysaccharides (LBP) have been proven to have the ability to regulate humoral and cellular immunity. To overcome the insufficiency of Alum, we explored a new adjuvant delivery system. The Lycium barbarum polysaccharides-loaded Particulate Alum via Pickering emulsion (LBPPE) was prepared by loading Alum on the squalene/water interphase following LBP was adsorbed on the Alum surface (Fig. 10). Similar to squalene, LBPPE possesses a good biosafety profile. LBPPE was spherical with uneven surface, which increased the possibility of efficient antigen adsorption on the surface and crack of LBPPE. And the result shown that the LBPPE had high antigen loading rate at approximately 90 %. In vivo experiments, LBPPE showed an excellent ability to recruit antigen-presenting cells (APCs) at the injection sites, activate dendritic cells in the lymph nodes. Then, in the evaluation of humoral immunity, LBPPE was able to effectively induce the production of IgG, IgG1, and IgG2a. Moreover, LBPPE significantly enhanced the expression and activation of T lymphocytes, and induced a strong immune memory T cells response. All the results above suggested that LBPPE is likely to provide promising insights toward a safe and efficient adjuvant platform for vaccines.

Targeting TLR4 during vaccination boosts MAdCAM-1+ lymphoid stromal cell activation and promotes the aged germinal center response

The failure to generate enduring humoral immunity after vaccination is a hallmark of advancing age. This can be attributed to a reduction in the germinal center (GC) response, which generates long-lived antibody-secreting cells that protect against (re)infection. Despite intensive investigation, the primary cellular defect underlying impaired GCs in aging has not been identified. Here, we used heterochronic parabiosis to demonstrate that GC formation was dictated by the age of the lymph node (LN) microenvironment rather than the age of the immune cells. Lymphoid stromal cells are a key determinant of the LN microenvironment and are also an essential component underpinning GC structure and function. Using mouse models, we demonstrated that mucosal adressin cell adhesion molecule-1 (MAdCAM-1)-expressing lymphoid stromal cells were among the first cells to respond to NP-KLH + Alum immunization, proliferating and up-regulating cell surface proteins such as podoplanin and cell adhesion molecules. This response was essentially abrogated in aged mice. By targeting TLR4 using adjuvants, we improved the MAdCAM-1⁺ stromal cell response to immunization. This correlated with improved GC responses in both younger adult and aged mice, suggesting a link between stromal cell responses to immunization and GC initiation. Using bone marrow chimeras, we also found that MAdCAM-1⁺ stromal cells could respond directly to TLR4 ligands. Thus, the age-associated defect in GC and stromal cell responses to immunization can be targeted to improve vaccines in older people.

Hematopoietic Cell Kinase (HCK) Is Essential for NLRP3 Inflammasome Activation and Lipopolysaccharide-Induced Inflammatory Response In Vivo

Activation of the NLRP3 inflammasome results in caspase 1 cleavage, which subsequently leads to IL-1β and IL-18 secretion, as well as pyroptosis, and aberrant activation of the inflammasome is involved in several diseases such as type 2 diabetes, atherosclerosis, multiple sclerosis, Parkinson's disease, and Alzheimer's disease. NLRP3 activity is regulated by various kinases. Genetic and pharmacological inhibition of the hematopoietic cell kinase (HCK), a member of the Src family of non-receptor tyrosine kinases (NRTKs) primarily expressed in myeloid cells, has previously been shown to ameliorate inflammation, indicating that it may be involved in the regulation of microglia function. However, the underlying mechanism is not known. Hence, in this study, we aimed to investigate the role of HCK in NLRP3 inflammasome activation. We demonstrated that HCK silencing inhibited NLRP3 inflammasome activation. Furthermore, the HCK-specific inhibitor, A419259, attenuated the release of IL-1β and caspase 1(P20) from the macrophages and microglia and reduced the formation of the apoptosis-associated speck-like protein with a CARD domain (ASC) oligomer. We also observed that HCK binds to full length NLRP3 and its NBD(NACHT) and LRR domains, but not to the PYD domain. In vivo, the HCK inhibitor attenuated the LPS-induced inflammatory response in the liver of LPS-challenged mice. Collectively, these results suggested that HCK plays a critical role in NLRP3 inflammasome activation. Our results will enhance current understanding regarding the effectiveness of HCK inhibitors for treating acute inflammatory diseases.

Novel xanthine oxidase-based cell model using HK-2 cell for screening antihyperuricemic functional compounds

Hyperuricemia is a metabolic disease caused by disorders of purine metabolism, the prevalence of which has increased worldwide. Here, a cell model for high uric acid production was established in vitro employing cultured human kidney cells (HK-2 cells), and its molecular basis was analyzed using gene expression profile. High performance liquid chromatography (HPLC) was used to monitor the content of metabolites in cell culture media. Adenosine addition was found to induce HK-2 cells to produce uric acid precursors (inosine and hypoxanthine). Furthermore, the cell model was verified by confirming the antihyperuricemic effect of the widely used antihyperuricemic drugs allopurinol, probenecid, and febuxostat, as well as reported bioactive peptides and amino acids, encompassing glutathione, tryptophan and carnosine, which significantly reduced uric acid production in the HK-2 cells (p < 0.05). RNA-Seq technology was used to perform a wide transcriptome analysis of the hyperuricemic cell model, and the results demonstrated that it has the potential to be used as a rapid and valid in vitro model to screen antihyperuricemic compounds that mimics in vivo cell growth patterns.

Immunogenicity and Immunodominance in Antibody Responses

A large number of vaccines exist that control many of the most important infectious diseases. Despite these successes, there remain many pathogens without effective prophylactic vaccines. Notwithstanding strong difference in the biology of these infectious agents, there exist common problems in vaccine design. Many infectious agents have highly variable surface antigens and/or unusually high antibody levels are required for protection. Such high variability may be addressed by using conserved epitopes and these are, however, usually difficult to display with the right conformation in an immunogenic fashion. Exceptionally high antibody titers may be achieved using life vectors or virus-like display of the epitopes. Hence, an important goal in modern vaccinology is to induce high antibody responses against fragile antigens.

Functional Programming of Innate Immune Cells in Response to Bordetella pertussis Infection and Vaccination

Despite widespread vaccination, B. pertussis remains one of the least controlled vaccine-preventable diseases. Although it is well known that acellular and whole cell pertussis vaccines induce distinct immune functionalities in memory cells, much less is known about the role of innate immunity in this process. In this review, we provide an overview of the known differences and similarities in innate receptors, innate immune cells and inflammatory signalling pathways induced by the pertussis vaccines either licensed or in development and compare this to primary infection with B. pertussis. Despite the crucial role of innate immunity in driving memory responses to B. pertussis, it is clear that a significant knowledge gap remains in our understanding of the early innate immune response to vaccination and infection. Such knowledge is essential to develop the next generation of pertussis vaccines with improved host defense against B. pertussis.

A Guide to IL-1 family cytokines in adjuvanticity

Growing awareness of the multiplicity of roles for the IL-1 family in immune regulation has prompted research exploring these cytokines in the context of vaccine-induced immunity. While tightly regulated, cytokines of the IL-1 family are normally released in response to cellular stress and in combination with other danger-/damage-associated molecular patterns (DAMPs), triggering potent local and systemic immune responses. In the context of infection or autoimmunity, engagement of IL-1 family receptors links robust innate responses to adaptive immunity. Clinical and experimental evidence has revealed that many vaccine adjuvants induce the release of one or multiple IL-1 family cytokines. The coordinated release of IL-1 family members in response to adjuvant-induced damage or cell death may be a determining factor in the transition from local inflammation to the induction of an adaptive response. Here, we analyse the effects of IL-1 family cytokines on innate and adaptive immunity with a particular emphasis on activation of antigen-presenting cells and induction of T cell-mediated immunity, and we address in detail the contribution of these cytokines to the modes of action of vaccine adjuvants including those currently approved for human use.

Adjuvanted influenza vaccines

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

Adjuvants

Developing new vaccines against emerging pathogens or pathogens where variability of antigenic sites presents a challenge, the inclusion of stimulators of the innate immune system is critical to mature the immune response in a way that allows high avidity recognition while preserving the ability to react to drifted serovars. The innate immune system is an ancient mechanism for recognition of nonself and the first line of defense against pathogen insult. By triggering innate receptors, adjuvants can boost responses to vaccines and enhance the quality and magnitude of the resulting immune response. This chapter: (1) describes the innate immune system, (2) provides examples of how adjuvants are formulated to optimize their effectiveness, and (3) presents examples of how adjuvants can improve outcomes of immunization.

Effects of immunomodulators on the response induced by vaccines against autoimmune diseases

A promising treatment for T-cell-mediated autoimmune diseases is the induction of immune tolerance by modulating the immune response against self-antigens, an objective that may be achieved by vaccination. There are two main types of vaccines currently under development. The tolerogenic vaccines, composed of proteins formed by a cytokine fused to a self-antigen, which usually induce tolerance by eliminating the T-cells that are immune reactive against the self-antigen. The immunogenic vaccines, comprised of a self-antigen plus a sole Th2 adjuvant either free or conjugated, that alleviate autoimmunity by switching the immune response against the self-antigen, from a damaging pro-inflammatory Th1/Th17 to an anti-inflammatory Th2 immunity. Another type of vaccines is the DNA vaccines, where cells transiently express the self-antigen encoded by DNA, which induces a Th2 immunity. Actually, DNA vaccines can benefit from the presence of an adjuvant that elicits a systemic sole Th2 immunity to enhance the initially weak immune response characteristic of these vaccines. While in the tolerogenic vaccines, cytokines are the endogenous immunomodulators, in the immunogenic vaccines, the adjuvants are exogenous agents that elicit Th2 immunity with a production of anti-inflammatory cytokines and antibodies against the self-antigen. Because the commonly used Th2 adjuvant alum, fails to induce an effective immunity in the elderly population, it is unlikely that it would be widely used. Another Th2 adjuvant, the oil/water emulsions mixed with the antigen, while effective in vaccines against infectious agents, due to potential aldehydes in their formulation may be not suitable for autoimmune vaccines. A unique compound is glatiramer, which seems to be both a random polypeptide antigen and an immune modulator that biases the response to Th2 immunity. Its mechanism of action seems to implicate binding to MHC-II, which alters the outcome of T-cell signaling, leading to anergy. Glatiramer, while effective in the treatment of multiple sclerosis has not shown efficacy in other autoimmune diseases. An important new group of promising sole Th2 adjuvants are the fucosylated glycans, which by binding to DC-SIGN bias dendritic cells to Th2 immunity while inhibiting Th1/Th7 immunities. These glycans are similar to those produced by parasitic helminths to prevent inflammatory responses by mammalian hosts. A novel group of sole Th2 adjuvants are some plant-derived fucosylated triterpene glycosides, which share the immune modulatory properties from the fucosylated glycans. These glycosides have also an aldehyde group that delivers an alternative co-stimulatory signal to T-cells, averting the anergy associated with aging due to the loss of the CD28 receptor on T-cells. Hence, the development of vaccines to treat and/or prevent autoimmune conditions and some proteopathies, will significantly benefit from the availability of new sole Th2 adjuvants that while inducing an anti-inflammatory immunity, they do not abrogate pro-inflammatory Th1/Th17 immunities.

Central Role of CD169+ Lymph Node Resident Macrophages in the Adjuvanticity of the QS-21 Component of AS01

Saponins represent a promising class of vaccine adjuvant. Together with the TLR4-ligand MPL, QS-21 is part of the Adjuvant System AS01, a key component of the malaria and zoster candidate vaccines that display demonstrated clinical efficacy. However, the mechanism of action of QS-21 in this liposomal formulation is poorly understood. Upon intra-muscular immunisation, we observed that QS-21 rapidly accumulated in CD169⁺ resident macrophages of the draining lymph node where it elicited a local innate immune response. Depletion of these cells abrogated QS-21-mediated innate cell recruitment to the lymph node, dendritic cell (DC) phenotypic maturation as well as the adjuvant effect on T-cell and antibody responses to co-administered antigens. DCs rather than lymph node-resident macrophages were directly involved in T-cell priming by QS-21, as revealed by the decrease in antigen-specific T-cell response in Batf3^−/− mice. Further analysis showed that the adjuvant effect of QS-21 depended on the integration of Caspase-1 and MyD88 pathways, at least in part through the local release of HMGB1. Taken together, this work unravels the key role of lymph node sentinel macrophage in controlling the adjuvant effect of a molecule proven to improve vaccine response in humans.

The Syk-NFAT-IL-2 Pathway in Dendritic Cells Is Required for Optimal Sterile Immunity Elicited by Alum Adjuvants

Despite a long history and extensive usage of insoluble aluminum salts (alum) as vaccine adjuvants, the molecular mechanisms underpinning Ag-specific immunity upon vaccination remain unclear. Dendritic cells (DCs) are crucial initiators of immune responses, but little is known about the molecular pathways used by DCs to sense alum and, in turn, activate T and B cells. In this article, we show that alum adjuvanticity requires IL-2 specifically released by DCs, even when T cell secretion of IL-2 is intact. We demonstrate that alum, as well as other sterile particulates, such as uric acid crystals, induces DCs to produce IL-2 following initiation of actin-mediated phagocytosis that leads to Src and Syk kinase activation, Ca²⁺ mobilization, and calcineurin-dependent activation of NFAT, the master transcription factor regulating IL-2 expression. Using chimeric mice, we show that DC-derived IL-2 is required for maximal Ag-specific proliferation of CD4⁺ T cells and optimal humoral responses following alum-adjuvanted immunization. These data identify DC-derived IL-2 as a key mediator of alum adjuvanticity in vivo and the Src-Syk pathway as a potential leverage point in the rational design of novel adjuvants.

Evaluation of different chemical adjuvants on an avian influenza H6 DNA vaccine in chickens

This study assessed the ability of three adjuvants (aluminium hydroxide, Essai (microparticle) and Phema (nanoparticle)) to enhance the immune response of chickens to an H6N2 avian influenza DNA vaccine. No haemagglutination inhibition antibody was detected following two intramuscular immunizations with the adjuvanted and non-adjuvanted pCAG-HAk vaccine, which has previously been shown to induce moderate H6 haemagglutinin antibody response in SPF chickens. Following virus challenge, neither the vaccinated group without adjuvant nor the Essai-adjuvanted group showed a statistically significant reduction in virus shedding in oropharyngeal and cloacal swabs compared with the naive control group. However, the aluminium hydroxide and Phema-adjuvanted groups significantly reduced the frequency of virus shedding in oropharyngeal swabs, indicating that these adjuvants appeared to further enhance the vaccine potency. Aluminium hydroxide holds promise as an adjuvant for enhancing DNA-induced immune response in chickens owing to its low price and safety record.

Toward understanding the mechanism underlying the strong adjuvant activity of aluminum salt nanoparticles

Aluminum salts such as aluminum oxyhydroxide and aluminum hydroxyphosphate are commonly used human vaccine adjuvants. In an effort to improve the adjuvant activity of aluminum salts, we previously showed that the adjuvant activity of aluminum oxyhydroxide nanoparticles is significantly more potent than that of aluminum oxyhydroxide microparticles. The present study was designed to (i) understand the mechanism underlying the potent adjuvant activity of aluminum oxyhydroxide nanoparticles, relative to microparticles, and (ii) to test whether aluminum hydroxyphosphate nanoparticles have a more potent adjuvant activity than aluminum hydroxyphosphate microparticles as well. In human THP-1 myeloid cells, wild-type and NLRP3-deficient, both aluminum oxyhydroxide nanoparticles and microparticles stimulate the secretion of proinflammatory cytokine IL-1β by activating NLRP3 inflammasome, although aluminum oxyhydroxide nanoparticles are more potent than microparticles, likely related to the higher uptake of the nanoparticles by the THP-1 cells than the microparticles. Aluminum hydroxyphosphate nanoparticles also have a more potent adjuvant activity than microparticles in helping a model antigen lysozyme to stimulate specific antibody response, again likely related to their stronger ability to activate the NLRP3 inflammasome.

Cytosolic Delivery of Liposomal Vaccines by Means of the Concomitant Photosensitization of Phagosomes

One of the greatest pharmaceutical challenges in vaccinology is the delivery of antigens to the cytosol of antigen-presenting cells (APCs) in order to allow for the stimulation of major histocompatibility complex (MHC) class I-restricted CD8(+) T-cell responses, which may act on intracellular infections or cancer. Recently, we described a novel method for cytotoxic T-lymphocyte (CTL) vaccination by combining antigens with a photosensitizer and light for cytosolic antigen delivery. The goal of the current project was to test this immunization method with particle-based formulations. Liposomes were prepared from dipalmitoylphosphatidylcholine and cholesterol, and the antigen ovalbumin (OVA) or the photosensitizer tetraphenyl chlorine disulfonate (TPCS2a) was separately encapsulated. C57BL/6 mice were immunized intradermally with OVA liposomes or a combination of OVA and TPCS2a liposomes, and light was applied the next day for activation of the photosensitizer resulting in cytosolic release of antigen from phagosomes. Immune responses were tested both after a prime only regime and after a prime-boost scheme with a repeat immunization 2 weeks post priming. Antigen-specific CD8(+) T-cell responses and antibody responses were analyzed ex vivo by flow cytometry and ELISA methods. The physicochemical stability of liposomes upon storage and light exposure was analyzed in vitro. Immunization with both TPCS2a- and OVA-containing liposomes greatly improved CD8(+) T-cell responses as compared to immunization without TPCS2a and as measured by proliferation in vivo and cytokine secretion ex vivo. In contrast, OVA-specific antibody responses (IgG1 and IgG2c) were reduced after immunization with TPCS2a-containing liposomes. The liposomal formulation protected the photosensitizer from light-induced inactivation during storage. In conclusion, the photosensitizer TPCS2a was successfully formulated in liposomes and enabled a shift from MHC class II to MHC class I antigen processing and presentation for stimulation of strong CD8(+) T-cell responses. Therefore, photosensitive particulate vaccines may have the potential to add to current vaccine practice a new method of vaccination that, as opposed to current vaccines, can stimulate strong CD8(+) T-cell responses.

Identification of QS-21 as an Inflammasome-activating Molecular Component of Saponin Adjuvants

Many immunostimulants act as vaccine adjuvants via activation of the innate immune system, although in many cases it is unclear which specific molecules contribute to the stimulatory activity. QS-21 is a defined, highly purified, and soluble saponin adjuvant currently used in licensed and exploratory vaccines, including vaccines against malaria, cancer, and HIV-1. However, little is known about the mechanisms of cellular activation induced by QS-21. We observed QS-21 to elicit caspase-1-dependent IL-1β and IL-18 release in antigen-presenting cells such as macrophages and dendritic cells when co-stimulated with the TLR4-agonist adjuvant monophosphoryl lipid A. Furthermore, our data suggest that the ASC-NLRP3 inflammasome is responsible for QS-21-induced IL-1β/IL-18 release. At higher concentrations, QS-21 induced macrophage and dendritic cell death in a caspase-1-, ASC-, and NLRP3-independent manner, whereas the presence of cholesterol rescued cell viability. A nanoparticulate adjuvant that contains QS-21 as part of a heterogeneous mixture of saponins also induced IL-1β in an NLRP3-dependent manner. Interestingly, despite the role NLRP3 plays for cellular activation in vitro, NLRP3-deficient mice immunized with HIV-1 gp120 and QS-21 showed significantly higher levels of Th1 and Th2 antigen-specific T cell responses and increased IgG1 and IgG2c compared with wild type controls. Thus, we have identified QS-21 as a nonparticulate single molecular saponin that activates the NLRP3 inflammasome, but this signaling pathway may contribute to decreased antigen-specific responses in vivo.

NOD-like receptors: versatile cytosolic sentinels

Nucleotide binding oligomerization domain (NOD)-like receptors are cytoplasmic pattern-recognition receptors that together with RIG-I-like receptor (retinoic acid-inducible gene 1), Toll-like receptor (TLR), and C-type lectin families make up the innate pathogen pattern recognition system. There are 22 members of NLRs in humans, 34 in mice, and even a larger number in some invertebrates like sea urchins, which contain more than 200 receptors. Although initially described to respond to intracellular pathogens, NLRs have been shown to play important roles in distinct biological processes ranging from regulation of antigen presentation, sensing metabolic changes in the cell, modulation of inflammation, embryo development, cell death, and differentiation of the adaptive immune response. The diversity among NLR receptors is derived from ligand specificity conferred by the leucine-rich repeats and an NH2-terminal effector domain that triggers the activation of different biological pathways. Here, we describe NLR genes associated with different biological processes and the molecular mechanisms underlying their function. Furthermore, we discuss mutations in NLR genes that have been associated with human diseases.

Biopersistence and brain translocation of aluminum adjuvants of vaccines

Aluminum oxyhydroxide (alum) is a crystalline compound widely used as an immunological adjuvant of vaccines. Concerns linked to the use of alum particles emerged following recognition of their causative role in the so-called macrophagic myofasciitis (MMF) lesion detected in patients with myalgic encephalomyelitis/chronic fatigue/syndrome. MMF revealed an unexpectedly long-lasting biopersistence of alum within immune cells in presumably susceptible individuals, stressing the previous fundamental misconception of its biodisposition. We previously showed that poorly biodegradable aluminum-coated particles injected into muscle are promptly phagocytosed in muscle and the draining lymph nodes, and can disseminate within phagocytic cells throughout the body and slowly accumulate in brain. This strongly suggests that long-term adjuvant biopersistence within phagocytic cells is a prerequisite for slow brain translocation and delayed neurotoxicity. The understanding of basic mechanisms of particle biopersistence and brain translocation represents a major health challenge, since it could help to define susceptibility factors to develop chronic neurotoxic damage. Biopersistence of alum may be linked to its lysosome-destabilizing effect, which is likely due to direct crystal-induced rupture of phagolysosomal membranes. Macrophages that continuously perceive foreign particles in their cytosol will likely reiterate, with variable interindividual efficiency, a dedicated form of autophagy (xenophagy) until they dispose of alien materials. Successful compartmentalization of particles within double membrane autophagosomes and subsequent fusion with repaired and re-acidified lysosomes will expose alum to lysosomal acidic pH, the sole factor that can solubilize alum particles. Brain translocation of alum particles is linked to a Trojan horse mechanism previously described for infectious particles (HIV, HCV), that obeys to CCL2, signaling the major inflammatory monocyte chemoattractant.

Activation of the NLRP3 inflammasome is not a feature of all particulate vaccine adjuvants

Particulate vaccine formulations, designed to improve the delivery of antigens to antigen-presenting cells (APCs) and to stimulate an immune response, have been shown to activate the NLRP3 inflammasome. This leads to the processing and secretion of interleukin (IL)-1β, which supports the recruitment of pro-inflammatory immune cells into the tissue and can therefore be beneficial for vaccine potency. Recent work suggested that this may be a common mechanism of action for all particulate formulations. The aim of this study was to investigate whether the activation of the NLRP3 inflammasome was common to many delivery systems. We prepared polymer-based chitosan nanoparticles (CNPs), lipid-based cubosomes, a water in oil emulsion of incomplete Freund's adjuvant (IFA) and alum formulations and examined inflammasome activation in vitro using murine bone-marrow-derived dendritic cells and human peripheral blood mononuclear cells and in vivo in mice. The formulations differed in their morphology, size and zeta-potential. Only the positively charged particles (CNPs and alum) were able to activate the inflammasome and increase the secretion of IL-1β. A decrease in the activation of the inflammasome with these particulates was observed when cathepsin B-mediated effects were blocked, implying a role of lysosomal rupture in the activation process. These findings demonstrate a role for the surface charge of particulates in the activation of the NLRP3 inflammasome, which should be considered when designing a novel vaccine formulation.

Inflammasome-dependent and -independent IL-18 production mediates immunity to the ISCOMATRIX adjuvant

Adjuvants are an essential component of modern vaccines and used for their ability to elicit immunity to coadministered Ags. Many adjuvants in clinical development are particulates, but how they drive innate and adaptive immune responses remains poorly understood. Studies have shown that a number of vaccine adjuvants activate inflammasome pathways in isolated APCs. However, the contribution of inflammasome activation to vaccine-mediated immunity in vivo remains controversial. In this study, we evaluated immune cell responses to the ISCOMATRIX adjuvant (IMX) in mice. Like other particulate vaccine adjuvants, IMX potently activated the NALP-3-ASC-Caspase-1 inflammasome in APCs, leading to IL-1β and IL-18 production. The IL-18R pathway, but not IL-1R, was required for early innate and subsequent cellular immune responses to a model IMX vaccine. APCs directly exposed to IMX underwent an endosome-mediated cell-death response, which we propose initiates inflammatory events locally at the injection site. Importantly, both inflammasome-related and -unrelated pathways contributed to IL-18 dependence in vivo following IMX administration. TNF-α provided a physiological priming signal for inflammasome-dependent IL-18 production by APCs, which correlated with reduced vaccine-mediated immune cell responses in TNF-α- or TNFR-deficient mice. Taken together, our findings highlight an important disconnect between the mechanisms of vaccine adjuvant action in vitro versus in vivo.

New directions in nicotine vaccine design and use

Clinical trials of nicotine vaccines suggest that they can enhance smoking cessation rates but do not reliably produce the consistently high serum antibody concentrations required. A wide array of next-generation strategies are being evaluated to enhance vaccine efficacy or provide antibody through other mechanisms. Protein conjugate vaccines may be improved by modifications of hapten or linker design or by optimizing hapten density. Conjugating hapten to viruslike particles or disrupted virus may allow exploitation of naturally occurring viral features associated with high immunogenicity. Conjugates that utilize different linker positions on nicotine can function as independent immunogens, so that using them in combination generates higher antibody concentrations than can be produced by a single immunogen. Nanoparticle vaccines, consisting of hapten, T cell help peptides, and adjuvants attached to a liposome or synthetic scaffold, are in the early stages of development. Nanoparticle vaccines offer the possibility of obtaining precise and consistent control of vaccine component stoichiometry and spacing and immunogen size and shape. Passive transfer of nicotine-specific monoclonal antibodies offers a greater control of antibody dose, the ability to give very high doses, and an immediate onset of action but is expensive and has a shorter duration of action than vaccines. Viral vector-mediated transfer of genes for antibody production can elicit high levels of antibody expression in animals and may present an alternative to vaccination or passive immunization if the long-term safety of this approach is confirmed. Next-generation immunotherapies are likely to be substantially more effective than first-generation vaccines.

Production of inflammatory cytokines in response to diphtheria-pertussis-tetanus (DPT), haemophilus influenzae type b (Hib), and 7-valent pneumococcal (PCV7) vaccines

Haemophilus influenzae type b (Hib) and 7-valent pneumococcal (PCV7) vaccines both became recommended in Japan in 2010. In this study, cytokine production was investigated in peripheral blood mononuclear cells (PBMCs) cultures stimulated with diphtheria and tetanus toxoids combined with acellular pertussis vaccine (DPT), Hib, and PCV7 separately or concurrent different combinations, all as final off-the-shelf vaccines without the individual vaccine components as controls. Higher IL-1β levels were produced when cultures were stimulated with PCV than with DPT or Hib, and the concurrent stimulation including PCV7 enhanced the production of IL-1β. Although Hib induced higher levels of IL-6, no significant difference was observed in IL-6 production with the concurrent stimulation. The concurrent stimulation with Hib/PCV7 and DPT/Hib/PCV7 produced higher levels of TNF-α and human G-CSF. Cytokine profiles were examined in serum samples obtained from 61 vaccine recipients with febrile reactions and 18 recipients without febrile illness within 24 h of vaccination. No significant difference was observed in cytokine levels of IL-1β, IL-4, IL-6, IL-10, IL-12, IFN-γ, MIP-1, TNF-α, and prostaglandin E2 (PGE2) in sera between the two groups. However, significantly higher levels of human G-CSF were observed in recipients with febrile illness than in those without febrile reactions. Further investigations of the significance of elevated serum G-CSF levels are required in vaccine recipients with febrile illness.

Inflammasomes and metabolic disease

Innate immune response pathways and metabolic pathways are evolutionarily conserved throughout species and are fundamental to survival. As such, the regulation of whole-body and cellular metabolism is intimately integrated with immune responses. However, the introduction of new variables to this delicate evolutionarily conserved physiological interaction can lead to deleterious consequences for organisms as a result of inappropriate immune responses. In recent decades, the prevalence and incidence of metabolic diseases associated with obesity have dramatically increased worldwide. As a recently acquired human characteristic, obesity has exposed the critical role of innate immune pathways in multiple metabolic pathophysiological processes. Here, we review recent evidence that highlights inflammasomes as critical sensors of metabolic perturbations in multiple tissues and their role in the progression of highly prevalent metabolic diseases.

[Demands and expectations of parents who refuse vaccinations and perspective of health professional on the refusal to vaccinate]

OBJECTIVES

To examine the opinions, beliefs and attitudes about vaccination, of parents who decide not to vaccinate their children. To determine the opinions and attitudes of the health professionals on the behaviour towards childhood vaccination.

METHOD

Qualitative research based on semi-structured interviews and focal groups in Granada, Spain, including parents who chose to not vaccinate their children, and healthcare professionals who can provide a technical point of view. An analysis was made of the semantic content, and answers were categorized in thematic units.

RESULTS

The parents argued on the benefit of suffering vaccine-preventable diseases in a natural way, without non-natural, aggressive or toxic products. Vaccination was considered unnecessary, if given adequate hygienic-sanitary conditions, effectiveness unproven and more dangerous than the diseases they prevent, especially the polyvalent vaccines. They believed that vaccination programs are moved by biased studies and interests other than prevention. Health care professionals believe that they had fears without scientific basis, which requires improving information systems.

CONCLUSIONS

Non-vaccinators are unaware of the benefit/risk ratio between the vaccination and the individual risk for preventable diseases, and ask for informed consent. Health care professionals believe that non-vaccinators' arguments are not correctly contrasted and expose the existence of failures in actual vaccination coverage and information registration systems. It was suggested to centralize registers and compare them in schools, working with local leaders and reporting regularly on the status of vaccine-preventable diseases.

NLRP3 controls Trypanosoma cruzi infection through a caspase-1-dependent IL-1R-independent NO production

Trypanosoma cruzi (T. cruzi) is an intracellular protozoan parasite and the etiological agent of Chagas disease, a chronic infectious illness that affects millions of people worldwide. Although the role of TLR and Nod1 in the control of T. cruzi infection is well-established, the involvement of inflammasomes remains to be elucidated. Herein, we demonstrate for the first time that T. cruzi infection induces IL-1β production in an NLRP3- and caspase-1-dependent manner. Cathepsin B appears to be required for NLRP3 activation in response to infection with T. cruzi, as pharmacological inhibition of cathepsin B abrogates IL-1β secretion. NLRP3^−/− and caspase1^−/− mice exhibited high numbers of T. cruzi parasites, with a magnitude of peak parasitemia comparable to MyD88^−/− and iNOS^−/− mice (which are susceptible models for T. cruzi infection), indicating the involvement of NLRP3 inflammasome in the control of the acute phase of T. cruzi infection. Although the inflammatory cytokines IL-6 and IFN-γ were found in spleen cells from NLRP3^−/− and caspase1^−/− mice infected with T. cruzi, these mice exhibited severe defects in nitric oxide (NO) production and an impairment in macrophage-mediated parasite killing. Interestingly, neutralization of IL-1β and IL-18, and IL-1R genetic deficiency demonstrate that these cytokines have a minor effect on NO secretion and the capacity of macrophages to control T. cruzi infection. In contrast, inhibition of caspase-1 with z-YVAD-fmk abrogated NO production by WT and MyD88^−/− macrophages and rendered them as susceptible to T. cruzi infection as NLRP3^−/− and caspase-1^−/− macrophages. Taken together, our results demonstrate a role for the NLRP3 inflammasome in the control of T. cruzi infection and identify NLRP3-mediated, caspase-1-dependent and IL-1R-independent NO production as a novel effector mechanism for these innate receptors.

Inflammasomes are cytosolic innate receptors that are emerging as central effectors in the control of infections and inflammatory pathologies. NLRP3 is the most studied member of inflammasomes with established role in the control of bacterial and viral infections. This manuscript describes original studies on the involvement of NLRP3 inflammasome in the control of Trypanosoma cruzi, the etiological agent of Chagas disease, a chronic infectious illness that affects millions of people in the world. T. cruzi activates NLRP3 inflammasome by a mechanism involving cathepsin B. NLRP3^−/− and caspase1^−/− mice display high parasitemia during acute phase of T. cruzi infection, which could be explained by a severe defect in the production of nitric oxide (NO) and in the impairment of their macrophages to control intracellular parasites. Interestingly, inhibition of caspase-1, but not the neutralization of IL-1β and IL-18, the best-studied caspase-1 substrates, abrogated NO production by WT and MyD88^−/− macrophages and rendered them as susceptible to T. cruzi infection as NLRP3^−/− macrophages. Together, our results indicate a caspase-1-dependent and IL-1β and IL-18-independent pathway for NO production as a new effector mechanism played by NLRP3 to control T. cruzi infection.

Immunomodulatory approaches for prevention and treatment of infectious diseases

With increasing pathogen resistance to antibiotics, population ageing, and threat of pandemics there is a strong interest in the development of new approaches for the treatment of infectious diseases. Immunomodulatory therapies are defined as interventions that target the host rather than the pathogen, modulating the immune response with the aim of disease prevention or treatment. Our growing understanding of the immune system continues to offer novel drug targets and approaches for immunomodulatory interventions. In this review we will cover prominent examples of immunomodulatory therapies already in clinical use, as well as the recent advances in the development of new immunomodulators in ongoing clinical trials.

Role of lysosome rupture in controlling Nlrp3 signaling and necrotic cell death

The Nod-like receptor, Nlrp3, has been linked to inflammatory diseases and adjuvant-mediated immune responses. A wide array of structurally diverse agents does not interact directly with Nlrp3, but is thought to activate the Nlrp3 inflammasome by inducing a common upstream signal, such as lysosome rupture. To test the connection between lysosome integrity and Nlrp3 signaling, we analyzed inflammasome activation following stimulation of murine macrophages with lysosome-destabilizing agents and pyroptosis inducers. Here we provide evidence that lysosomal rupture and the corresponding release of lysosomal hydrolases is an early event in macrophages exposed to the lysosome-destabilizing adjuvants LLOMe and alum. Lysosome rupture preceded cell death induction mediated by these agents and was associated with the degradation of low-molecular weight proteins, including the inflammasome component caspase-1. Proteolysis of caspase-1 was controlled by specific cathepsins, but was independent of autocatalytic processes and Nlrp3 signaling. Consistent with these findings, lysosome-disrupting agents triggered only minimal caspase-1 activation and failed to cause caspase-1-dependent cell death (pyroptosis), generally associated with Nlrp3 signaling. In contrast, lysosome rupture was a late event in macrophages exposed to prototypical pyroptosis inducers. These agents triggered extensive Nlrp3 signaling prior to lysosome rupture with only minimal impact on the cellular proteome. Taken together, our findings suggest that lysosome impairment triggers a cascade of events culminating in cell death but is not crucial for Nlrp3 signaling. The significant differences observed between lysosome-disrupting agents and pyroptosis inducers might explain the distinct immunologic responses associated with these compounds.

Evaluation of pyroptosis in macrophages using cytosolic delivery of purified flagellin

Pyroptosis is a molecularly controlled form of cell death that exhibits some features of apoptosis as well of necrosis. Pyroptosis is induced by inflammasome-activated caspase-1 or caspase-11 (caspase-4 in humans), as a result of distinct pathogenic or damage stimuli. Although pyroptosis displays some morphological and biochemical features of apoptosis, it has an inflammatory outcome due to the loss of plasma membrane integrity and the consequent release of intracellular contents, reminiscent to necrosis. Here, we use cytosolic delivery of purified flagellin as an experimental tool to trigger pyroptosis and describe potential methods to study this form of cell death. Finally, we discuss the advantages and limitations of these methods.

Cathepsin-mediated necrosis controls the adaptive immune response by Th2 (T helper type 2)-associated adjuvants

Immunologic adjuvants are critical components of vaccines, but it remains unclear how prototypical adjuvants enhance the adaptive immune response. Recent studies have shown that necrotic cells could trigger an immune response. Although most adjuvants have been shown to be cytotoxic, this activity has traditionally been considered a side effect. We set out to test the role of adjuvant-mediated cell death in immunity and found that alum, the most commonly used adjuvant worldwide, triggers a novel form of cell death in myeloid leukocytes characterized by cathepsin-dependent lysosome-disruption. We demonstrated that direct lysosome-permeabilization with a soluble peptide, Leu-Leu-OMe, mimics the alum-like form of necrotic cell death in terms of cathepsin dependence and cell-type specificity. Using a combination of a haploid genetic screen and cathepsin-deficient cells, we identified specific cathepsins that control lysosome-mediated necrosis. We identified cathepsin C as critical for Leu-Leu-OMe-induced cell death, whereas cathepsins B and S were required for alum-mediated necrosis. Consistent with a role of necrotic cell death in adjuvant effects, Leu-Leu-OMe replicated an alum-like immune response in vivo, characterized by dendritic cell activation, granulocyte recruitment, and production of Th2-associated antibodies. Strikingly, cathepsin C deficiency not only blocked Leu-Leu-OMe-mediated necrosis but also impaired Leu-Leu-OMe-enhanced immunity. Together our findings suggest that necrotic cell death is a powerful mediator of a Th2-associated immune response.

The rhapsody of NLRPs: master players of inflammation...and a lot more

The Nucleotide-binding oligomerization domain, Leucine-rich Repeat and Pyrin domain containing (NLRP) family and corresponding inflammasomes are important intracellular sensors of microbial pathogens and stress signals that promote caspase-1-mediated release of IL-1β and IL-18. Studies using targeted disruption of NLRP1 and NLRP3 have revealed key roles for these inflammasomes in innate immunity and inflammation, as well as in autoimmune diseases, metabolic disorders, and cancers. The newly identified family members NLRP6, NLRP10, and NLRP12 are emerging as important molecules regulating gut homeostasis in mouse models, as well as being correlated to human diseases. Here, we review our current knowledge of NLRP1 and NLRP3 biology, from molecular structure, function, and proposed models of activation to associations with several human disorders. New insights into novel NLRPs that act as regulators of intestinal immunity are also discussed.

Evaluation of the protective immune response induced in mice by immunization with Schistosoma mansoni schistosomula tegument (Smteg) in association with CpG-ODN

In schistosomiasis, the current control strategy does not prevent reinfection, therefore, vaccine strategies are essential to combat the Schistosoma mansoni. The efficacy vaccine depends on parasite stage and effective adjuvant. We have recently demonstrated that S. mansoni schistosomula tegument (Smteg) is able to activate dendritic cells up regulate CD40 and CD86 molecules and induce a partial protection in mice (43-48%) when formulated with Freund's adjuvant. In this study we evaluated the ability of Smteg + alum or Smteg + alum + CpG-ODN to induce protection in mice. Our results demonstrate that Smteg + alum + CpG-ODN induced a partial reduction in worm burden (43.1%), reduction in the number of eggs eliminated in the feces. The protective response was associated with a predominant Th1 type of immune response, with increased production of specific IgG2c, IFN-γ and TNF-α, B cells proliferation and CD4 cells and macrophages activation.

Immune response to vaccine adjuvants during the first year of life

Subunit vaccine formulations often include adjuvants that primarily stimulate innate immune cells. While young infants represent the major target population for vaccination, effective immunization in this age group remains a challenge. Many parameters of innate immune responses differ quantitatively and qualitatively from newborns to infants and adults, revealing a highly regulated developmental program. Herein, we discuss the potential implications of innate immune ontogeny for the activity of adjuvants contained in licensed infant vaccines, as well as future directions for rational design of adjuvanted vaccines for this age group.

[Role of allergen-specific immunotherapy (desensitization) for the treatment of allergies in Germany. Current situation]

Allergen-specific immunotherapy (SIT, desensitization) is applied monthly with subcutaneous injections (SCIT) or sublingually (SLIT) with droplets or tablets on a daily basis. Numerous immunological changes during SIT induce long-lasting tolerance. Efficacy has been demonstrated by a number of controlled studies for insect venom hypersensitivity (SCIT), allergic rhinoconjunctivitis (SCIT, SLIT particularly in grass pollen allergy), and allergic asthma (SCIT > SLIT). SIT is indicated in children and adults with severe allergic reactions from insect venoms (e.g., bee, wasp) or cumbersome symptoms from pollen, house dust mites or mold allergens and proven immediated-type allergy. Contraindications must be considered individually. SIT is performed for 3 years, in case of venom allergy 3-5 years. Severe systemic reactions are rare after SCIT. After SLIT rather local allergic symptoms of short duration occur in the mouth and throat. At present, the number prescriptions for SIT has decreased due to inadequate reimbursement of allergy-related services (diagnostics, therapies, monitoring). In the future, inferior medical care of allergic patients in Germany is expected, who until now have benefited from the preventive effects of SIT (reduced risk of developing asthma and new allergic sensitizations).

Mucosal vaccine adjuvants update

Mucosal vaccination, capable of inducing protective immune responses both in the mucosal and systemic immune compartments, has many advantages and is regarded as a blue ocean in the vaccine industry. Mucosal vaccines can offer lower costs, better accessability, needle-free delivery, and higher capacity of mass immunizations during pandemics. However, only very limited number of mucosal vaccines was approved for human use in the market yet. Generally, induction of immune responses following mucosal immunization requires the co-administration of appropriate adjuvants that can initiate and support the effective collaboration between innate and adaptive immunity. Classically, adjuvant researches were rather empirical than keenly scientific. However, during last several years, fundamental scientific achievements in innate immunity have been translated into the development of new mucosal adjuvants. This review focuses on recent developments in the concepts of adjuvants and innate immunity, mucosal immunity with special interest of vaccine development, and basic and applied researches in mucosal adjuvant.

Intranasal vaccination with murabutide enhances humoral and mucosal immune responses to a virus-like particle vaccine

Murabutide (MB) is a synthetic immunomodulator recognized by the nucleotide-binding oligomerization domain-containing protein 2 (NOD2) receptor on mammalian cells. MB has previously been approved for testing in multiple human clinical trials to determine its value as an antiviral therapeutic, and as an adjuvant for injected vaccines. We have found a new use for this immunomodulator; it functions as a mucosal adjuvant that enhances immunogenicity of virus-like particles (VLP) administered intranasally. MB enhanced Norwalk virus (NV) VLP-specific IgG systemically and IgA production at distal mucosal sites following intranasal (IN) vaccination. A dose escalation study identified 100 µg as the optimal MB dosage in mice, based on the magnitude of VLP-specific IgG, IgG1, IgG2a and IgA production in serum and VLP-specific IgA production at distal mucosal sites. IN vaccination using VLP with MB was compared to IN delivery VLP with cholera toxin (CT) or gardiquimod (GARD) and to parenteral VLP delivery with alum; the MB groups were equivalent to CT and GARD and superior to alum in inducing mucosal immune responses and stimulated equivalent systemic VLP-specific antibodies. These data support the further testing of MB as a potent mucosal adjuvant for inducing robust and durable antibody responses to non-replicating subunit vaccines.

Type II NKT cells facilitate Alum-sensing and humoral immunity

Alum-based adjuvants facilitate vaccine-driven humoral immunity, but their mechanism of action remains poorly understood. Herein, we report that lack of type II NKT cells is associated with intact, mature B cells but dampened humoral immunity following immunization with Alum-adsorbed T-dependent antigen. Type II NKT cells facilitated production of IL-4, IL-5, IL-10, IL-13, and antibody by LN and splenocyte cultures following Alum/antigen administration in vivo and antigen restimulation in vitro. Addition of IL-4 and IL-5 to type II NKT-deficient cultures restored in vitro antibody production. Intracellular staining revealed that Alum-primed type II NKT cells coordinated IL-4 secretion by T cells. Alum did not significantly affect CD1d expression in vivo, but addition of CD1d-blocking mAb diminished cytokine production and in vitro antibody production. Type II NKT cells therefore function as part of the Alum-sensing apparatus and in a CD1d-dependent manner, facilitate T(H)2-driven humoral immunity. This may have important consequences for understanding the mechanism of action of Alum-containing vaccines.

Systematic identification of small molecule adjuvants

INTRODUCTION

Adjuvants potentiate immune responses, reducing the amount and dosing frequency of antigen required for inducing protective immunity. Adjuvants are of special importance when considering subunit, epitope-based or more unusual vaccine formulations lacking significant innate immunogenicity. While numerous adjuvants are known, only a few are licensed for human use; principally alum, and squalene-based oil-in-water adjuvants. Alum, the most commonly used, is suboptimal. There are many varieties of adjuvant: proteins, oligonucleotides, drug-like small molecules and liposome-based delivery systems with intrinsic adjuvant activity being perhaps the most prominent.

AREAS COVERED

This article focuses on small molecules acting as adjuvants, with the author reviewing their current status while highlighting their potential for systematic discovery and rational optimisation. Known small molecule adjuvants (SMAs) can be synthetically complex natural products, small oligonucleotides or drug-like synthetic molecules. The author provides examples of each class, discussing adjuvant mechanisms relevant to SMAs, and exploring the high-throughput discovery of SMAs.

EXPERT OPINION

SMAs, particularly synthetic drug-like adjuvants, are amenable to the plethora of drug-discovery techniques able to optimise the properties of biologically active small molecules. These range from laborious synthetic modifications to modern, rational, effort-efficient computational approaches, such as QSAR and structure-based drug design. In principal, any property or characteristic can thus be designed in or out of compounds, allowing us to tailor SMAs to specific biological functions, such as targeting specific cells or pathways, in turn affording the power to tailor SMAs to better address different diseases.

Nucleic acid sensing at the interface between innate and adaptive immunity in vaccination

The demand is currently high for new vaccination strategies, particularly to help combat problematic intracellular pathogens, such as HIV and malarial parasites. In the past decade, the identification of host receptors that recognize pathogen-derived nucleic acids has revealed an essential role for nucleic acid sensing in the triggering of immunity to intracellular pathogens. This Review first addresses our current understanding of the nucleic acid-sensing immune machinery. We then explain how the study of nucleic acid-sensing mechanisms not only has revealed their central role in driving the responses mediated by many current vaccines, but is also revealing how they could be harnessed for the design of new vaccines.

Ontogeny of Toll-like and NOD-like receptor-mediated innate immune responses in Papua New Guinean infants

Studies addressing the ontogeny of the innate immune system in early life have reported mainly on Toll-like receptor (TLR) responses in infants living in high-income countries, with little or even no information on other pattern recognition receptors or on early life innate immune responses in children living under very different environmental conditions in less-developed parts of the world. In this study, we describe whole blood innate immune responses to both Toll-like and nucleotide-binding oligomerization domain (NOD)-like receptor agonists including the widely used vaccine adjuvant ‘alum’ in a group of Papua New Guinean infants aged 1–3 (n = 18), 4–6 (n = 18), 7–12 (n = 21) and 13–18 (n = 10) months old. Depending on the ligands and cytokines studied, different age-related patterns were found: alum-induced IL-1β and CXCL8 responses were found to significantly decline with increasing age; inflammatory (IL-6, IL-1β, IFN-γ) responses to TLR2 and TLR3 agonists increased; and IL-10 responses remained constant or increased during infancy, while TNF-α responses either declined or remained the same. We report for the first time that whole blood innate immune responses to the vaccine adjuvant alum decrease with age in infancy; a finding that may imply that the adjuvant effect of alum in pediatric vaccines could be age-related. Our findings further suggest that patterns of innate immune development may vary between geographically diverse populations, which in line with the ‘hygiene hypothesis’ particularly involves persistence of innate IL-10 responses in populations experiencing higher infectious pressure.

Alum-adjuvanted H5N1 whole virion inactivated vaccine (WIV) enhanced inflammatory cytokine productions

Alum-adjuvanted H5 whole virion inactivated vaccine (WIV) was licensed for adults in Japan but induced marked febrile reactions with significantly stronger antibody responses in children. In this study, the mechanisms behind the different responses were investigated. Lymphocytes were obtained from 25 healthy subjects who were not immunized with H5 vaccine, to examine the innate immune impact of the various vaccine formulations, analyzing the cytokine production profile stimulated with alum adjuvant alone, alum-adjuvanted H5 WIIV, plain H5 WIV, and H5 split vaccine. Alum adjuvant did not induce cytokine production, but H5 split induced IFN-γ and TNF-α. H5 WIV induced IL-6, IL-17, TNF-α, MCP-1, IFN-γ, and IFN-α. An extremely low level of IL-1β was produced in response to H5 WIV, and alum-adjuvanted H5 WIV enhanced IL-1β production, with similar levels of other cytokines stimulated with H5 WIV. Enhanced production of cytokines induced by alum-adjuvanted H5 WIV may be related to the higher incidence of febrile reactions with stronger immune responses in children but it should be further investigated why efficient immune responses with febrile illness were observed only in young children.