Adjuvants for human vaccines

Particle size analyses of polydisperse liposome formulations with a novel multispectral advanced nanoparticle tracking technology

Liposomes are potent adjuvant constituents for licensed vaccines and vaccine candidates and carriers for drug delivery. Depending on the method of preparation, liposomes vary in size distribution, either forming uniform small size vesicles or a heterogeneous mixture of small to large vesicles. Importantly, differences in liposomal size have been demonstrated to induce differential immune responses. Determination of particle size distribution could therefore be crucial for the efficacy and stability of vaccine formulations. We compared the techniques of dynamic light scattering, laser diffraction, and conventional nanoparticle tracking analysis with a novel multispectral advanced nanoparticle tracking analysis (MANTA) for particle size determination of mono- and polydisperse liposomes. MANTA reported an average 146 nm size of monodisperse liposomes but showed a multimodal distribution of polydisperse liposomes with continuous sizes from 50 to 2000 nm. However, approximately 95% of particles were in the size range of 50-1500 nm and only few particles were identified in the 1500-2000 nm range for the investigated volume. Based on our results, we conclude that MANTA is the most suitable approach and can serve as stand-alone technique for particle size characterization of heterogeneous liposome samples in the 50-2000 nm size range.

Novos adjuvantes vacinais: importante ferramenta para imunoterapia da leishmaniose visceral

Atualmente, muitas das vacinas em desenvolvimento são aquelas compostas de proteínas antigênicas individuais de parasitas ou uma combinação de vários antígenos individuais que são produzidos como produtos recombinantes obtidos por técnicas de biologia molecular. Dentre elas a Leish-111f e sua variação Leish-110f tem ganhado destaque na proteção contra a LV e LC e alcançaram estudos de fase II em seres humanos. A eficácia de uma vacina é otimizada pela adição de adjuvantes imunológicos. No entanto, embora os adjuvantes tenham sido usados por mais de um século, até o momento, apenas alguns adjuvantes são aprovados para o uso em humanos, a maioria destinada a melhorar a eficácia da vacina e a produção de anticorpos protetores específicos do antígeno. Os mecanismos de ação dos adjuvantes imunológicos são diversos, dependendo da sua natureza química e molecular sendo capazes de ativar células imunes especificas que conduzem a respostas imunes inatas e adaptativas melhoradas. Embora o mecanismo de ação molecular detalhado de muitos adjuvantes ainda seja desconhecido, a descoberta de receptores Toll-like (TLRs) forneceu informações críticas sobre o efeito imunoestimulador de numerosos componentes bacterianos que envolvem interação com receptores TLRs, mostrando que estes ligantes melhoram tanto a qualidade como a quantidade de respostas imunes adaptativas do hospedeiro quando utilizadas em formulações de vacinais direcionadas para doenças. O potencial desses adjuvantes de TLR em melhorar o design e os resultados de várias vacinas está em constante evolução, à medida que novos agonistas são descobertos e testados em modelos experimentais e estudos clínicos de vacinação. Nesta revisão, é apresentado um resumo do progresso recente no desenvolvimento de proteínas recombinantes de segunda geração e adjuvantes de TLR, sendo o foco principal nos TLR4 e suas melhorias.

Foamy matters: an update on Quillaja saponins and their use as immunoadjuvants

Immunoadjuvant Quillaja spp. tree saponins stimulate both cellular and humoral responses, significantly widening vaccine target pathogen spectra. Host toxicity of specific saponins, fractions and extracts may be rather low and further reduced using lipid-based delivery systems. Saponins contain a hydrophobic central aglycone decorated with several sugar residues, posing a challenge for viable chemical synthesis. These, however, may provide simpler analogs. Saponin chemistry affords characteristic interactions with cell membranes, which are essential for its mechanism of action. Natural sources include Quillaja saponaria barks and, more recently, Quillaja brasiliensis leaves. Sustainable large-scale supply can use young plants grown in clonal gardens and elicitation treatments. Quillaja genomic studies will most likely buttress future synthetic biology-based saponin production efforts.

A prophylactic α-Gal-based glycovaccine effectively protects against murine acute Chagas disease

Chagas disease (ChD), caused by the hemoflagellate parasite Trypanosoma cruzi, affects six to seven million people in Latin America. Lately, it has become an emerging public health concern in nonendemic regions such as North America and Europe. There is no prophylactic or therapeutic vaccine as yet, and current chemotherapy is rather toxic and has limited efficacy in the chronic phase of the disease. The parasite surface is heavily coated by glycoproteins such as glycosylphosphatidylinositol (GPI)-anchored mucins (tGPI-mucins), which display highly immunogenic terminal nonreducing α-galactopyranosyl (α-Gal)-containing glycotopes that are entirely absent in humans. The immunodominant tGPI-mucin α-Gal glycotope, the trisaccharide Galα1,3Galβ1,4GlcNAc (Galα3LN), elicits high levels of protective T. cruzi-specific anti-α-Gal antibodies in ChD patients in both the acute and chronic phases. Although glycoconjugates are the major parasite glycocalyx antigens, they remain completely unexplored as potential ChD vaccine candidates. Here we investigate the efficacy of the T. cruzi immunodominant glycotope Galα3LN, covalently linked to a carrier protein (human serum albumin (HSA)), as a prophylactic vaccine candidate in the acute model of ChD, using the α1,3-galactosyltransferase-knockout (α1,3GalT-KO) mouse, which mimics the human immunoresponse to α-Gal glycotopes. Animals vaccinated with Galα3LN-HSA were fully protected against lethal T. cruzi challenge by inducing a strong anti-α-Gal antibody-mediated humoral response. Furthermore, Galα3LN-HSA-vaccinated α1,3GalT-KO mice exhibited significant reduction (91.7–99.9%) in parasite load in all tissues analyzed, cardiac inflammation, myocyte necrosis, and T cell infiltration. This is a proof-of-concept study to demonstrate the efficacy of a prophylactic α-Gal-based glycovaccine for experimental acute Chagas disease.

A vaccine candidate derived from an immunodominant parasitic glycan could offer a much-needed preventive therapy for Chagas disease. The disease, caused by the parasite Trypanosoma cruzi, is endemic to Latin America and an emergent threat to North America and Europe. Current therapies are few, poorly efficacious, and toxic. Igor Almeida, from the University of Texas at El Paso, United States, and his team created a candidate which presents a host with T. cruzi surface-derived α-galactose-containing (α-Gal) glycan covalently linked to a carrier protein. Parasite-derived α-Gal-containing proteins are known to be highly immune-stimulating to humans but were previously unexplored as prophylactics. In a mouse model designed to mimic the human response to Chagas disease, vaccinated animals had a strong antibody response and were fully protected against lethal exposure to T. cruzi. The results offer a promising candidate for future research and validate the method used in this proof-of-concept study.

Induction and decay of functional complement-fixing antibodies by the RTS,S malaria vaccine in children, and a negative impact of malaria exposure

BACKGROUND

Leading malaria vaccine, RTS,S, is based on the circumsporozoite protein (CSP) of sporozoites. RTS,S confers partial protection against malaria in children, but efficacy wanes relatively quickly after primary immunization. Vaccine efficacy has some association with anti-CSP IgG; however, it is unclear how these antibodies function, and how functional antibodies are induced and maintained over time. Recent studies identified antibody-complement interactions as a potentially important immune mechanism against sporozoites. Here, we investigated whether RTS,S vaccine-induced antibodies could function by interacting with complement.

METHODS

Serum samples were selected from children in a phase IIb trial of RTS,S/AS02_A conducted at two study sites of high and low malaria transmission intensity in Manhiça, Mozambique. Samples following primary immunization and 5-year post-immunization follow-up time points were included. Vaccine-induced antibodies were characterized by isotype, subclass, and epitope specificity, and tested for the ability to fix and activate complement. We additionally developed statistical methods to model the decay and determinants of functional antibodies after vaccination.

RESULTS

RTS,S vaccination induced anti-CSP antibodies that were mostly IgG1, with some IgG3, IgG2, and IgM. Complement-fixing antibodies were effectively induced by vaccination, and targeted the central repeat and C-terminal regions of CSP. Higher levels of complement-fixing antibodies were associated with IgG that equally recognized both the central repeat and C-terminal regions of CSP. Older age and higher malaria exposure were significantly associated with a poorer induction of functional antibodies. There was a marked decay in functional complement-fixing antibodies within months after vaccination, as well as decays in IgG subclasses and IgM. Statistical modeling suggested the decay in complement-fixing antibodies was mostly attributed to the waning of anti-CSP IgG1, and to a lesser extent IgG3.

CONCLUSIONS

We demonstrate for the first time that RTS,S can induce complement-fixing antibodies in young malaria-exposed children. The short-lived nature of functional responses mirrors the declining vaccine efficacy of RTS,S over time. The negative influence of age and malaria exposure on functional antibodies has implications for understanding vaccine efficacy in different settings. These findings provide insights into the mechanisms and longevity of vaccine-induced immunity that will help inform the future development of highly efficacious and long-lasting malaria vaccines.

Cyclic Dinucleotide-Adjuvanted Dengue Virus Nonstructural Protein 1 Induces Protective Antibody and T Cell Responses

Endothelial dysfunction and vascular leak, pathogenic hallmarks of severe dengue disease, are directly triggered by dengue virus (DENV) nonstructural protein 1 (NS1). Previous studies have shown that immunization with NS1, as well as passive transfer of NS1-immune serum or anti-NS1 mAb, prevent NS1-mediated lethality in vivo. In this study, we evaluated the immunogenicity and protective capacity of recombinant DENV NS1 administered with cyclic dinucleotides (CDNs), potent activators of innate immune pathways and highly immunogenic adjuvants. Using both wild-type C57BL/6 mice and IFN-α/β receptor-deficient mice, we show that NS1-CDN immunizations elicit serotype-specific and cross-reactive Ab and T cell responses. Furthermore, NS1-CDN vaccinations conferred significant homotypic and heterotypic protection from DENV2-induced morbidity and mortality. In addition, we demonstrate that high anti-NS1 Ab titers are associated with protection, supporting the role of humoral responses against DENV NS1 as correlates of protection. These findings highlight the potential of CDN-based adjuvants for inducing Ab and T cell responses and validate NS1 as an important candidate for dengue vaccine development.

The vaccine adjuvant MPLA activates glycolytic metabolism in mouse mDC by a JNK-dependent activation of mTOR-signaling

INTRODUCTION

The detoxified TLR4-ligand MPLA is a successfully used adjuvant in clinically approved vaccines. However, its capacity to activate glycolytic metabolism in mDC and the influence of MPLA-induced metabolic changes on cytokine secretion are unknown.

AIM

To analyze the capacity of MPLA to activate mDC metabolism and the mechanisms contributing to MPLA-induced metabolism activation and cytokine secretion.

METHODS

C57BL/6 bone-marrow-derived myeloid dendritic cells (mDCs) were stimulated with LPS or MPLA and analyzed for intracellular signaling, cytokine secretion, and metabolic state. mDC were pre-treated with rapamycin (mTOR-inhibitor), U0126, SP600125, SB202190 (MAPK kinase inhibitors), as well as dexamethasone (MAPK- and NFκB-inhibitor) and analyzed for MPLA-induced cytokine secretion and cell metabolic state.

RESULTS

Stimulation of mDCs with either LPS or MPLA resulted in a pronounced, mTOR-dependent activation of glucose metabolism characterized by induction of the Warburg Effect, increased glucose consumption from the culture medium, as well as release of LDH. Compared to LPS, MPLA induced significantly lower cytokine secretion. The activation of mDC metabolism was comparable between LPS- and MPLA-stimulated mDCs. The MPLA-induced cytokine secretion could be partially inhibited using mTOR-, MAP kinase-, and NFκB-inhibitors, whereas the activation of glucose metabolism was shown to depend on both mTOR- and JNK-signaling.

SUMMARY

The MPLA-induced activation of glycolytic metabolism in mouse mDC was shown to depend on a JNK-mediated activation of mTOR-signaling, while both MAPK- and NFB-signaling contributed to pro-inflammatory cytokine secretion. Understanding the mechanisms by which MPLA activates dendritic cells will both improve our understanding of its adjuvant properties and contribute to the future development and safe application of this promising adjuvant.

The adjuvant effect of C60(OH)22 nanoparticles promoting both humoral and cellular immune responses to HCV recombinant proteins

Hepatitis c virus (HCV) infection is one of major causes for chronic liver diseases worldwide and could lead to death. Development of effective HCV vaccines is a powerful auxiliary method of existing treatments. Adjuvants are necessary for modern vaccines to promote immune responses. Among the various nanomaterials that have been developed, multihydroxylated fullerene (C₆₀(OH)₂₂) has been proved as an efficient adjuvant for human immunodeficiency virus DNA vaccine. Here, we utilized three types of HCV recombinant proteins as antigens to investigate the activity of C₆₀(OH)₂₂ as a protein vaccine adjuvant. The proteins were carried by C₆₀(OH)₂₂ in a way of surface adsorption and self-assemble encapsulation. C₆₀(OH)₂₂ at a relatively low dose was sufficient to promote both humoral and cellular immune responses to HCV protein antigens and reduce the usage of antigen. These results demonstrated the positive adjuvant properties of C₆₀(OH)₂₂ when applied to protein vaccines.

DAMP-Inducing Adjuvant and PAMP Adjuvants Parallelly Enhance Protective Type-2 and Type-1 Immune Responses to Influenza Split Vaccination

Recently, it was reported that 2-hydroxypropyl-β-cyclodextrin (HP-β-CyD), a common pharmaceutical additive, can act as a vaccine adjuvant to enhance protective type-2 immunogenicity to co-administered seasonal influenza split vaccine by inducing host-derived damage-associated molecular patterns (DAMPs). However, like most other DAMP-inducing adjuvants such as aluminum hydroxide (Alum), HP-β-CyD may not be sufficient for the induction of protective type-1 (cellular) immune responses, thereby leaving room for improvement. Here, we demonstrate that a combination of HP-β-CyD with a humanized TLR9 agonist, K3 CpG-ODN, a potent pathogen-associated molecular pattern (PAMP), enhanced the protective efficacy of the co-administered influenza split vaccine by inducing antigen-specific type-2 and type-1 immune responses, respectively. Moreover, substantial antigen-specific IgE induction by HP-β-CyD, which can cause an allergic response to immunized antigen was completely suppressed by the addition of K3 CpG-ODN. Furthermore, HP-β-CyD- and K3 CpG-ODN-adjuvanted influenza split vaccination protected the mice against lethal challenge with high doses of heterologous influenza virus, which could not be protected against by single adjuvant vaccines. Further experiments using gene deficient mice revealed the unique immunological mechanism of action in vivo, where type-2 and type-1 immune responses enhanced by the combined adjuvants were dependent on TBK1 and TLR9, respectively, indicating their parallel signaling pathways. Finally, the analysis of immune responses in the draining lymph node suggested that HP-β-CyD promotes the uptake of K3 CpG-ODN by plasmacytoid dendritic cells and B cells, which may contributes to the activation of these cells and enhanced production of IgG2c. Taken together, the results above may offer potential clinical applications for the combination of DAMP-inducing adjuvant and PAMP adjuvant to improve vaccine immunogenicity and efficacy by enhancing both type-2 and type-1 immune responses in a parallel manner.

Recent clinical trends in Toll-like receptor targeting therapeutics

Toll‐like receptors (TLRs) are germline‐encoded receptors that are central to innate and adaptive immune responses. Owing to their vital role in inflammation, TLRs are rational targets in clinics; thus, many ligands and biologics have been reported to overcome the progression of various inflammatory and malignant conditions and support the immune system. For each TLR, at least one, and often many, drug formulations are being evaluated. Ligands reported as stand‐alone drugs may also be reported based on their use in combinatorial therapeutics as adjuvants. Despite their profound efficacy in TLR‐modulation in preclinical studies, multiple drugs have been terminated at different stages of clinical trials. Here, TLR modulating drugs that have been evaluated in clinical trials are discussed, along with their mode of action, suggestive failure reasons, and ways to improve the clinical outcomes. This review presents recent advances in TLR‐targeting drugs and provides directions for more successful immune system manipulation.

Make It Simple: (SR-A1+TLR7) Macrophage Targeted NANOarchaeosomes

Hyperhalophilic archaebacteria exclusively produce sn2,3 diphytanylglycerol diether archaeolipids, unique structures absent in bacteria and eukaryotes. Nanovesicles made of archaeolipids known as nanoarchaeosomes (nanoARC), possess highly stable bilayers, some of them displaying specific targeting ability. Here we hypothesize that nanoARC made from Halorubrum tebenquichense archaebacteria, may constitute efficient carriers for the TLR7 agonist imiquimod (IMQ). NanoARC-IMQ takes advantage of the intense interaction between IMQ and the highly disordered, poorly fluid branched archaeolipid bilayers, rich in archaeol analog of methyl ester of phosphatidylglycerophosphate (PGP-Me), a natural ligand of scavenger receptor A1 (SR-A1). This approach lacks complex manufacture steps required for bilayers labeling, enabling future analytical characterization, batch reproducibility, and adaptation to higher scale production. SR-A1 mediated internalization of particulate material is mostly targeted to macrophages and is extensive because it is not submitted to a negative feedback. A massive and selective intracellular delivery of IMQ may concentrate its effect specifically into the endosomes, where the TLR7 is expressed, magnifying its immunogenicity, at the same time reducing its systemic bioavailability, and therefore it's in vivo adverse effects. NanoARC-IMQ (600-900 nm diameter oligolamellar vesicles of ~-43 mV Z potential) were heavily loaded with IMQ at ~44 μg IMQ/mg phospholipids [~20 folds higher than the non-SR-A1 ligand soyPC liposomes loaded with IMQ (LIPO-IMQ)]. In vitro, nanoARC-IMQ induced higher TNF-α and IL-6 secretion by J774A1 macrophages compared to same dose of IMQ and same lipid dose of LIPO-IMQ. In vivo, 3 subcutaneous doses of nanoARC-IMQ+ 10 μg total leishmania antigens (TLA) at 50 μg IMQ per Balb/C mice, induced more pronounced DTH response, accompanied by a nearly 2 orders higher antigen-specific systemic IgG titers than IMQ+TLA and LIPO-IMQ. The isotype ratio of nanoARC-IMQ+TLA remained ~0.5 indicating, the same as IMQ+TLA, a Th2 biased response distinguished by a pronounced increase in antibody titers, without negative effects on splenocytes lymphoproliferation, with a potential CD8+LT induction 10 days after the last dose. Overall, this first approach showed that highly SR-A1 mediated internalization of heavily loaded nanoARC-IMQ, magnified the effect of IMQ on TLR7 expressing macrophages, leading to a more intense in vivo immune response.

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

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

Overcoming immunogenicity issues of HIV p24 antigen by the use of innovative nanostructured lipid carriers as delivery systems: evidences in mice and non-human primates

HIV is one of the deadliest pandemics of modern times, having already caused 35 million deaths around the world. Despite the huge efforts spent to develop treatments, the virus cannot yet be eradicated and continues to infect new people. Spread of the virus remains uncontrolled, thus exposing the worldwide population to HIV danger, due to the lack of efficient vaccines. The latest clinical trials describe the challenges associated with developing an effective prophylactic HIV vaccine. These immunological obstacles will only be overcome by smart and innovative solutions applied to the design of vaccine formulations. Here, we describe the use of nanostructured lipid carriers (NLC) for the delivery of p24 protein as a model HIV antigen, with the aim of increasing its immunogenicity. We have designed vaccine formulations comprising NLC grafted with p24 antigen, together with cationic NLC optimized for the delivery of immunostimulant CpG. This tailored system significantly enhanced immune responses against p24, in terms of specific antibody production and T-cell activation in mice. More importantly, the capacity of NLC to induce specific immune responses against this troublesome HIV antigen was further supported by a 7-month study on non-human primates (NHP). This work paves the way toward the development of a future HIV vaccine, which will also require the use of envelope antigens.

To date, HIV vaccines have resulted in poor or absent protection. A team led by Fabrice P. Navarro at the CEA LETI use the conserved HIV capsid protein p24 vectorized into cationic nanostructured lipid carriers (NLC-p24) along with NLC-delivered CpG. Owing to their small size, NLCs gain access to lymph nodes and deliver antigen directly to antigen presenting cells. Anti-p24 responses have been associated with effective HIV control, making them an attractive vaccine antigen, but they are poorly immunogenic. NLC-p24 shows a good safety profile while at the same time being able to elicit robust humoral and cellular immune responses in both mice and Cynomolgus macaques. NLC-mediated delivery of both p24 and CpG results in more effective immune stimulation than delivery of free antigen and adjuvant. These findings demonstrate the possibility of priming effective responses to a potent but otherwise poorly immunogenic HIV antigen.

A combination of TLR-4 agonist and saponin adjuvants increases antibody diversity and protective efficacy of a recombinant West Nile Virus antigen

Members of the Flaviviridae family are the leading causes of mosquito-borne viral disease worldwide. While dengue virus is the most prevalent, the recent Zika virus outbreak in the Americas triggered a WHO public health emergency, and yellow fever and West Nile viruses (WNV) continue to cause regional epidemics. Given the sporadic nature of flaviviral epidemics both temporally and geographically, there is an urgent need for vaccines that can rapidly provide effective immunity. Protection from flaviviral infection is correlated with antibodies to the viral envelope (E) protein, which encodes receptor binding and fusion functions. TLR agonist adjuvants represent a promising tool to enhance the protective capacity of flavivirus vaccines through dose and dosage reduction and broadening of antiviral antibody responses. This study investigates the ability to improve the immunogenicity and protective capacity of a promising clinical-stage WNV recombinant E-protein vaccine (WN-80E) using a novel combination adjuvant, which contains a potent TLR-4 agonist and the saponin QS21 in a liposomal formulation (SLA-LSQ). Here, we show that, in combination with WN-80E, optimized SLA-LSQ is capable of inducing long-lasting immune responses in preclinical models that provide sterilizing protection from WNV challenge, reducing viral titers following WNV challenge to undetectable levels in Syrian hamsters. We have investigated potential mechanisms of action by examining the antibody repertoire generated post-immunization. SLA-LSQ induced a more diverse antibody response to WNV recombinant E-protein antigen than less protective adjuvants. Collectively, these studies identify an adjuvant formulation that enhances the protective capacity of recombinant flavivirus vaccines.

Engineering a Rugged Nanoscaffold To Enhance Plug-and-Display Vaccination

Nanoscale organization is crucial to stimulating an immune response. Using self-assembling proteins as multimerization platforms provides a safe and immunogenic system to vaccinate against otherwise weakly immunogenic antigens. Such multimerization platforms are generally based on icosahedral viruses and have led to vaccines given to millions of people. It is unclear whether synthetic protein nanoassemblies would show similar potency. Here we take the computationally designed porous dodecahedral i301 60-mer and rationally engineer this particle, giving a mutated i301 (mi3) with improved particle uniformity and stability. To simplify the conjugation of this nanoparticle, we employ a SpyCatcher fusion of mi3, such that an antigen of interest linked to the SpyTag peptide can spontaneously couple through isopeptide bond formation (Plug-and-Display). SpyCatcher-mi3 expressed solubly to high yields in Escherichia coli, giving more than 10-fold greater yield than a comparable phage-derived icosahedral nanoparticle, SpyCatcher-AP205. SpyCatcher-mi3 nanoparticles showed high stability to temperature, freeze-thaw, lyophilization, and storage over time. We demonstrate approximately 95% efficiency coupling to different transmission-blocking and blood-stage malaria antigens. Plasmodium falciparum CyRPA was conjugated to SpyCatcher-mi3 nanoparticles and elicited a high avidity antibody response, comparable to phage-derived virus-like particles despite their higher valency and RNA cargo. The simple production, precise derivatization, and exceptional ruggedness of this nanoscaffold should facilitate broad application for nanobiotechnology and vaccine development.

Unique depot formed by an oil based vaccine facilitates active antigen uptake and provides effective tumour control

Background

Oil emulsions are commonly used as vaccine delivery platforms to facilitate slow release of antigen by forming a depot at the injection site. Antigen is trapped in the aqueous phase and as the emulsion degrades in vivo the antigen is passively released. DepoVax™ is a unique oil based delivery system that directly suspends the vaccine components in the oil diluent that forces immune cells to actively take up components from the formulation in the absence of passive release. The aim of this study was to use magnetic resonance imaging (MRI) with additional biological markers to evaluate and understand differences in clearance between several different delivery systems used in peptide-based cancer vaccines.

Methods

C57BL/6 mice were implanted with a cervical cancer model and vaccinated 5 days post-implant with either DepoVax (DPX), a water-in-oil emulsion (w/o), a squalene oil-in-water emulsion (squal o/w) or a saponin/liposome emulsion (sap/lip) containing iron oxide-labeled targeted antigen. MRI was then used to monitor antigen clearance, the site of injection, tumour and inguinal lymph node volumes and other gross anatomical changes. HLA-A2 transgenic mice were also vaccinated to evaluate immune responses of human directed peptides.

Results

We demonstrated differences in antigen clearance between DPX and w/o both in regard to how quickly the antigen was cleared and the pattern in which it was cleared. We also found differences in lymph node responses between DPX and both squal o/w and sap/lip.

Conclusions

These studies underline the unique mechanism of action of this clinical stage vaccine delivery system.

Electronic supplementary material

The online version of this article (10.1186/s12929-018-0413-9) contains supplementary material, which is available to authorized users.

Immunostimulatory activity of water-extractable polysaccharides from Cistanche deserticola as a plant adjuvant in vitro and in vivo

A safe and effective vaccine adjuvant is important in modern vaccines. Various Chinese herbal polysaccharides can activate the immune system. Cistanche deserticola (CD) is a traditional Chinese herb and an adjuvant candidate. Here, we confirmed that water-extractable polysaccharides of CD (WPCD) could modulate immune responses in vitro and in vivo. In a dose-dependent manner, WPCD significantly promoted the maturation and function of murine marrow-derived dendritic cells (BM-DCs) through up-regulating the expression levels of MHC-II, CD86, CD80, and CD40, allogenic T cell proliferation, and the yields of IL-12 and TNF-α via toll-like receptor4 (TLR4), as indicated by in vitro experiments. In addition, its immunomodulatory activity was also observed in mice. WPCD effectively improved the titers of IgG, IgG1 and IgG2a and markedly enhanced the proliferation of T and B cells, the production of IFN-γ and IL-4 in CD4+ T cells and the expression level of IFN-γ in CD8+ T cells better than Alum. Furthermore, WPCD could markedly up-regulate the expression levels of CD40 and CD80 on DCs in spleen and down-regulate the Treg frequency. The study suggests that polysaccharides of Cistanche deserticola are a safe and effective vaccine adjuvant for eliciting both humoral immunity and cellular immunity by activating DCs via TLR4 signaling pathway.

Subcutaneous administration CpG-ODNs acts as a potent adjuvant for an HIV-1-tat-based vaccine candidate to elicit cellular immunity in BALB/c mice

OBJECTIVE

To evaluate the combined effects of CpG oligodeoxynucleotides (CpG-ODNs) adjuvant and subcutaneous injection route on efficacy of a HIV-1-tat DNA vaccine candidate using BALB/c mice as an animal model.

RESULTS

Evaluation of cellular and humoral immunity of mice injected subcutaneously with HIV-1-tat gene cloned into a pcDNA3.1 vector indicated that significant levels of IFN-γ cytokine secretion (900 pg/ml), lymphocyte proliferation (2.5 stimulation index) and IgG_2a (1.45 absorbance 450 nm) production could be achieved. These indicators of stimulated cellular immunity were elicited 2 weeks after the last injection (P < 0.05).

CONCLUSIONS

Formulation of HIV-1-tat DNA vaccine candidate with CpG-ODNs as an adjuvant while administrated subcutaneously are a promising approach to induce effective cellular immunity responses against HIV-1 infection.

Protein nanovaccine confers robust immunity against Toxoplasma

We designed and produced a self-assembling protein nanoparticle. This self-assembling protein nanoparticle contains five CD8+ HLA-A03-11 supertypes-restricted epitopes from antigens expressed during Toxoplasma gondii's lifecycle, the universal CD4+ T cell epitope PADRE, and flagellin as a scaffold and TLR5 agonist. These CD8+ T cell epitopes were separated by N/KAAA spacers and optimized for proteasomal cleavage. Self-assembling protein nanoparticle adjuvanted with TLR4 ligand-emulsion GLA-SE were evaluated for their efficacy in inducing IFN-γ responses and protection of HLA-A*1101 transgenic mice against T. gondii. Immunization, using self-assembling protein nanoparticle-GLA-SE, activated CD8+ T cells to produce IFN-γ. Self-assembling protein nanoparticle-GLA-SE also protected HLA-A*1101 transgenic mice against subsequent challenge with Type II parasites. Hence, combining CD8+ T cell-eliciting peptides and PADRE into a multi-epitope protein that forms a nanoparticle, administered with GLA-SE, leads to efficient presentation by major histocompatibility complex Class I and II molecules. Furthermore, these results suggest that activation of TLR4 and TLR5 could be useful for development of vaccines that elicit T cells to prevent toxoplasmosis in humans.

The anti-influenza M2e antibody response is promoted by XCR1 targeting in pig skin

XCR1 is selectively expressed on a conventional dendritic cell subset, the cDC1 subset, through phylogenetically distant species. The outcome of antigen-targeting to XCR1 may therefore be similar across species, permitting the translation of results from experimental models to human and veterinary applications. Here we evaluated in pigs the immunogenicity of bivalent protein structures made of XCL1 fused to the external portion of the influenza virus M2 proton pump, which is conserved through strains and a candidate for universal influenza vaccines. Pigs represent a relevant target of such universal vaccines as pigs can be infected by swine, human and avian strains. We found that cDC1 were the only cell type labeled by XCR1-targeted mCherry upon intradermal injection in pig skin. XCR1-targeted M2e induced higher IgG responses in seronegative and seropositive pigs as compared to non-targeted M2e. The IgG response was less significantly enhanced by CpG than by XCR1 targeting, and CpG did not further increase the response elicited by XCR1 targeting. Monophosphoryl lipid A with neutral liposomes did not have significant effect. Thus altogether M2e-targeting to XCR1 shows promises for a trans-species universal influenza vaccine strategy, possibly avoiding the use of classical adjuvants.

Transcutaneous immunization with a novel imiquimod nanoemulsion induces superior T cell responses and virus protection

BACKGROUND

Transcutaneous immunization (TCI) is a novel vaccination strategy utilizing the skin associated lymphatic tissue to induce immune responses. TCI using a cytotoxic T lymphocyte (CTL) epitope and the Toll-like receptor 7 (TLR7) agonist imiquimod mounts strong CTL responses by activation and maturation of skin-derived dendritic cells (DCs) and their migration to lymph nodes. However, TCI based on the commercial formulation Aldara only induces transient CTL responses that needs further improvement for the induction of durable therapeutic immune responses.

OBJECTIVE

Therefore we aimed to develop a novel imiquimod solid nanoemulsion (IMI-Sol) for TCI with superior vaccination properties suited to induce high quality T cell responses for enhanced protection against infections.

METHODS

TCI was performed by applying a MHC class I or II restricted epitope along with IMI-Sol or Aldara (each containing 5% Imiquimod) on the shaved dorsum of C57BL/6, IL-1R, Myd88, Tlr7 or Ccr7 deficient mice. T cell responses as well as DC migration upon TCI were subsequently analyzed by flow cytometry. To determine in vivo efficacy of TCI induced immune responses, CTL responses and frequency of peptide specific T cells were evaluated on day 8 or 35 post vaccination and protection in a lymphocytic choriomeningitis virus (LCMV) infection model was assessed.

RESULTS

TCI with the imiquimod formulation IMI-Sol displayed equal skin penetration of imiquimod compared to Aldara, but elicited superior CD8⁺ as well as CD4⁺ T cell responses. The induction of T-cell responses induced by IMI-Sol TCI was dependent on the TLR7/MyD88 pathway and independent of IL-1R. IMI-Sol TCI activated skin-derived DCs in skin-draining lymph nodes more efficiently compared to Aldara leading to enhanced protection in a LCMV infection model.

CONCLUSION

Our data demonstrate that IMI-Sol TCI can overcome current limitations of previous imiquimod based TCI approaches opening new perspectives for transcutaneous vaccination strategies and allowing the use of this enhanced cutaneous drug-delivery system to be tailored for the improved prevention and treatment of infectious diseases and cancers.

A Formulated TLR7/8 Agonist is a Flexible, Highly Potent and Effective Adjuvant for Pandemic Influenza Vaccines

Since 1997, highly pathogenic avian influenza viruses of the H5N1 subtype have been transmitted from avian hosts to humans. The severity of H5N1 infection in humans, as well as the sporadic nature of H5N1 outbreaks, both geographically and temporally, make generation of an effective vaccine a global public health priority. An effective H5N1 vaccine must ultimately provide protection against viruses from diverse clades. Toll-like receptor (TLR) agonist adjuvant formulations have a demonstrated ability to broaden H5N1 vaccine responses in pre-clinical models. However, many of these agonist molecules have proven difficult to develop clinically. Here, we describe comprehensive adjuvant formulation development of the imidazoquinoline TLR-7/8 agonist 3M-052, in combination with H5N1 hemagglutinin (HA) based antigens. We find that 3M-052 in multiple formulations protects both mice and ferrets from lethal H5N1 homologous virus challenge. Furthermore, we conclusively demonstrate the ability of 3M-052 adjuvant formulations to broaden responses to H5N1 HA based antigens, and show that this broadening is functional using a heterologous lethal virus challenge in ferrets. Given the extensive clinical use of imidazoquinoline TLR agonists for other indications, these studies identify multiple adjuvant formulations which may be rapidly advanced into clinical trials in an H5N1 vaccine.

Antibody Epitopes Identified in Critical Regions of Dengue Virus Nonstructural 1 Protein in Mouse Vaccination and Natural Human Infections

Dengue is a global public health problem and is caused by four dengue virus (DENV) serotypes (DENV1-4). A major challenge in dengue vaccine development is that cross-reactive anti-DENV Abs can be protective or potentially increase disease via Ab-dependent enhancement. DENV nonstructural protein 1 (NS1) has long been considered a vaccine candidate as it avoids Ab-dependent enhancement. In this study, we evaluated survival to challenge in a lethal DENV vascular leak model in mice immunized with NS1 combined with aluminum and magnesium hydroxide, monophosphoryl lipid A + AddaVax, or Sigma adjuvant system+CpG DNA, compared with mice infected with a sublethal dose of DENV2 and mice immunized with OVA (negative control). We characterized Ab responses to DENV1, 2, and 3 NS1 using an Ag microarray tiled with 20-mer peptides overlapping by 15 aa and identified five regions of DENV NS1 with significant levels of Ab reactivity in the NS1 + monophosphoryl lipid A + AddaVax group. Additionally, we profiled the Ab responses to NS1 of humans naturally infected with DENV2 or DENV3 in serum samples from Nicaragua collected at acute, convalescent, and 12-mo timepoints. One region in the wing domain of NS1 was immunodominant in both mouse vaccination and human infection studies, and two regions were identified only in NS1-immunized mice; thus, vaccination can generate Abs to regions that are not targeted in natural infection and could provide additional protection against lethal DENV infection. Overall, we identified a small number of immunodominant regions, which were in functionally important locations on the DENV NS1 protein and are potential correlates of protection.

Quercetin exhibits adjuvant activity by enhancing Th2 immune response in ovalbumin immunized mice

Quercetin, one of the most abundant of plant flavonoids, has been studied with a great deal of attention over the last several decades mainly for its properties in inflammation and allergy. In this study, we are reporting for the first time the in vivo immunostimulatory activity of quercetin in ovalbumin immunized Balb/c mice. Administration of quercetin (50mg/kg body weight) along with ovalbumin antigen showed increased ovalbumin specific serum IgG antibody titres in comparison to the control group (p<0.05). Quercetin administration not only showed predominance of Th2 immune response by increasing the IgG1 antibody titres, but also increased the infiltration of CD11c⁺ dendritic cells in the mouse peritoneum and also increased LPS activated IL-1β and nitric oxide (NO) production by peritoneal macrophages. Expression of Tbx21, GATA-3 and Oct-2 proteins also enhanced in splenocytes of quercetin administered mice. Quercetin also did not cause any hemolysis in human RBCs. Overall, our findings strongly demonstrate the novel in vivo immunostimulatory and adjuvant potentials of quercetin.

Synthesis and immunological evaluation of a low molecular weight saccharide with TLR-4 agonist activity

The paucity of FDA approved adjuvants renders the synthesis, characterization, and use of new compounds as vaccine adjuvants, a necessity. For this purpose, a novel saccharide analog has been synthesized from glucosamine, pyruvylated galactose and 1,4-cyclohexanediol and its biological efficacy was determined in innate immune cells. More specifically, we assessed the production of pro-inflammatory cytokines from the murine monocyte cell line, Raw 264.7 and from C57 BL/6 mouse peritoneal macrophages following exposure to the saccharide analog. Our data conclude that the novel saccharide has immunostimulatory activity on mouse macrophages as indicated by the elevated levels of IL-6 and TNF-α in culture supernatants. This effect was TLR-4-dependent but TLR-2-independent. Our data, suggest TLR-4 agonism; a key feature of vaccine adjuvants.

Vaccination with toxofilin DNA in combination with an alum-monophosphoryl lipid A mixed adjuvant induces significant protective immunity against Toxoplasma gondii

BACKGROUND

A widely prevalent disease, toxoplasmosis poses serious health threats to both humans and animals; therefore, development of an ideal DNA vaccine against Toxoplasma gondii is needed eagerly. The purpose of the present study is to assess the protective efficacy of a DNA vaccine encoding the T. gondii toxofilin gene (pEGFP-toxofilin). In addition, toxofilin DNA vaccine combined with the individual adjuvants, alum or monophosphoryl lipid A (MPLA), or a mixture of alum-MPLA adjuvant were screened for their ability to enhance antibody responses.

METHODS

Using bioinformatics, we analyzed the gene and amino acid sequences of the toxofilin protein, recognizing and identifying several potential linear B and T helper (Th)-1 cell epitopes. BALB/c mice were immunized three times with either toxofilin DNA vaccine alone or in combination with the adjuvants such as alum, MPLA or an alum-MPLA mixture. The systemic immune response was evaluated by cytokine, the percentage of CD4 (+) and CD8 (+) T cells and specific antibody measurement. Two weeks after the last immunization, protective efficacy was evaluated by challenging intraperitoneally with 1 × 10⁴ tachyzoites of T. gondii or intragastrically with 20 cysts of T. gondii PRU strain.

RESULTS

All experimentally immunized mice developed strong humoral and cellular immune responses compared with the control groups. Moreover, by comparison with the non-adjuvant toxofilin DNA vaccine group, adding alum adjuvant to toxofilin DNA vaccine resulted in an increase in humoral response and a skewed Th2 response. However, the MPLA adjuvant with toxofilin DNA vaccine induced significantly enhanced humoral and Th1-biased immune responses. Importantly, the co-administration of alum-MPLA adjuvant in combination with the toxofilin DNA vaccine shifted the Th2 immune response to a Th1 response compared with the alum-toxofilin group, and elicited the strongest humoral and Th1 responses among all the groups. At the same time, a longer survival time and less cyst amounts against T. gondii infection were also observed in the alum-MPLA-toxofilin group in comparison with single or no adjuvant groups.

CONCLUSIONS

Toxoplasma gondii toxofilin is a promising vaccine candidate that warrants further development. Co-administration of the alum-MPLA adjuvant mixture with DNA vaccine could effectively enhance immunogenicity and strongly skew the cellular immune response towards a Th1 phenotype.

Comparative Transcriptome Profiles of Human Blood in Response to the Toll-like Receptor 4 Ligands Lipopolysaccharide and Monophosphoryl Lipid A

Monophosphoryl lipid A (MPLA), a less toxic derivative of lipopolysaccharide (LPS), is employed as a vaccine adjuvant and is under investigation as a non-specific immunomodulator. However, the differential response of human leukocytes to MPLA and LPS has not been well characterized. The goal of this study was to compare the differential transcriptomic response of human blood to LPS and MPLA. Venous blood from human volunteers was stimulated with LPS, MPLA or vehicle. Gene expression was determined using microarray analysis. Among 21,103 probes profiled, 136 and 130 genes were differentially regulated by LPS or MPLA, respectively. Seventy four genes were up-regulated and 9 were down-regulated by both ligands. The remaining genes were differentially induced by either agent. Ingenuity Pathway Analysis predicted that LPS and MPLA share similar upstream regulators and have comparable effects on canonical pathways and cellular functions. However, some pro-inflammatory cytokine and inflammasome-associated transcripts were more strongly induced by LPS. In contrast, only the macrophage-regulating chemokine CCL7 was preferentially up-regulated by MPLA. In conclusion, LPS and MPLA induce similar transcriptional profiles. However, LPS more potently induces pro-inflammatory cytokine and inflammasome-linked transcripts. Thus, MPLA is a less potent activator of the pro-inflammatory response but retains effective immunomodulatory activity.

Immunological effects of different types of synthetic CpG oligodeoxynucleotides on porcine cells

The agonists of toll-like receptor 9, synthetic oligodeoxynucleotides (ODNs) containing CpG sequences, stimulate innate and adaptive immune responses in humans and a variety of animal species.

Screening Immunomodulators To Skew the Antigen-Specific Autoimmune Response

Current therapies to treat autoimmune diseases often result in side effects such as nonspecific immunosuppression. Therapies that can induce antigen-specific immune tolerance provide an opportunity to reverse autoimmunity and mitigate the risks associated with global immunosuppression. In an effort to induce antigen-specific immune tolerance, co-administration of immunomodulators with autoantigens has been investigated in an effort to reprogram autoimmunity. To date, identifying immunomodulators that may skew the antigen-specific immune response has been ad hoc at best. To address this need, we utilized splenocytes obtained from mice with experimental autoimmune encephalomyelitis (EAE) in order to determine if certain immunomodulators may induce markers of immune tolerance following antigen rechallenge. Of the immunomodulatory compounds investigated, only dexamethasone modified the antigen-specific immune response by skewing the cytokine response and decreasing T-cell populations at a concentration corresponding to a relevant in vivo dose. Thus, antigen-educated EAE splenocytes provide an ex vivo screen for investigating compounds capable of skewing the antigen-specific immune response, and this approach could be extrapolated to antigen-educated cells from other diseases or human tissues.

Saponaria officinalis L. extract: Surface active properties and impact on environmental bacterial strains

Plant-derived surfactants are characterised by low toxicity, high biodegradability and environmental compatibility. They therefore have many applications; for instance, they can be used in bioremediation to accelerate biodegradation processes, especially of hydrophobic pollutants. This paper analyses the properties of an extract from Saponaria officinalis L. containing saponins and its impact on bacterial strains isolated from soil, as well as its potential for application in hydrocarbon bioremediation. The tested extract from Saponaria officinalis L. contains gypsogenin, hederagenin, hydroxyhederagenin and quillaic acid aglycone structures and demonstrates good emulsification properties. Contact with the extract led to modification of bacterial cell surface properties. A decrease in cell surface hydrophobicity and an increase in membrane permeability were recorded in the experiments. An increase of up to 63% in diesel oil biodegradation was also recorded for Pseudomonas putida DA1 on addition of 1gL^-1 of saponins from Saponaria officinalis L. Saponaria extract showed no toxic impact on the tested environmental bacterial strains at the concentration used in the biodegradation process.

Co-Delivery of Imiquimod and Plasmid DNA via an Amphiphilic pH-Responsive Star Polymer that Forms Unimolecular Micelles in Water

Dual functional unimolecular micelles based on a pH-responsive amphiphilic star polymer β-CD-(PLA-b-PDMAEMA-b-PEtOxMA)21 have been developed for the co-delivery of imiquimod and plasmid DNA to dendritic cells. The star polymer with well-defined triblock arms was synthesized by combining activator regenerated by electron-transfer atom-transfer radical polymerization with ring-opening polymerization. Dissipative particle dynamics simulation showed that core-mesophere-shell-type unimolecular micelles could be formed. Imiquimod-loaded micelles had a drug loading of 1.6 wt % and a larger average size (28 nm) than blank micelles (19 nm). The release of imiquimod in vitro was accelerated at the mildly acidic endolysosomal pH (5.0) in comparison to physiologic pH (7.4). Compared with blank micelles, a higher N:P ratio was required for imiquimod-loaded micelles to fully condense DNA into micelleplexes averaging 200⁻400 nm in size. In comparison to blank micelleplexes, imiquimod-loaded micelleplexes of the same N:P ratio displayed similar or slightly higher efficiency of gene transfection in a mouse dendritic cell line (DC2.4) without cytotoxicity. These results suggest that such pH-responsive unimolecular micelles formed by the well-defined amphiphilic star polymer may serve as promising nano-scale carriers for combined delivery of hydrophobic immunostimulatory drugs (such as imiquimod) and plasmid DNA with potential application in gene-based immunotherapy.

Influenza Vaccine Research funded by the European Commission FP7-Health-2013-Innovation-1 project

Due to influenza viruses continuously displaying antigenic variation, current seasonal influenza vaccines must be updated annually to include the latest predicted strains. Despite all the efforts put into vaccine strain selection, vaccine production, testing, and administration, the protective efficacy of seasonal influenza vaccines is greatly reduced when predicted vaccine strains antigenically mismatch with the actual circulating strains. Moreover, preparing for a pandemic outbreak is a challenge, because it is unpredictable which strain will cause the next pandemic. The European Commission has funded five consortia on influenza vaccine development under the Seventh Framework Programme for Research and Technological Development (FP7) in 2013. The call of the EU aimed at developing broadly protective influenza vaccines. Here we review the scientific strategies used by the different consortia with respect to antigen selection, vaccine delivery system, and formulation. The issues related to the development of novel influenza vaccines are discussed.

Modular Peptide Amphiphile Micelles Improving an Antibody-Mediated Immune Response to Group A Streptococcus

Inducing a strong and specific immune response is the hallmark of a successful vaccine. Nanoparticles have emerged as promising vaccine delivery devices to discover and elicit immune responses. Fine-tuning a nanoparticle vaccine to create an immune response with specific antibody and other cellular responses is influenced by many factors such as shape, size, and composition. Peptide amphiphile micelles are a unique biomaterials platform that can function as a modular vaccine delivery system, enabling control over many of these important factors and delivering payloads more efficiently to draining lymph nodes. In this study, the modular properties of peptide amphiphile micelles are utilized to improve an immune response against a Group A Streptococcus B cell antigen (J8). The hydrophobic/hydrophilic interface of peptide amphiphile micelles enabled the precise entrapment of amphiphilic adjuvants which were found to not alter micelle formation or shape. These heterogeneous micelles significantly enhanced murine antibody responses when compared to animals vaccinated with nonadjuvanted micelles or soluble J8 peptide supplemented with a classical adjuvant. The heterogeneous micelle induced antibodies also showed cross-reactivity with wild-type Group A Streptococcus providing evidence that micelle-induced immune responses are capable of identifying their intended pathogenic targets.

Development of Improved Vaccine Adjuvants Based on the Saponin Natural Product QS-21 through Chemical Synthesis

Vaccines based on molecular subunit antigens are increasingly being investigated due to their improved safety and more precise targeting compared to classical whole-pathogen vaccines. However, subunit vaccines are inherently less immunogenic; thus, coadministration of an adjuvant to increase the immunogenicity of the antigen is often necessary to elicit a potent immune response. QS-21, an immunostimulatory saponin natural product, has been used as an adjuvant in conjunction with various vaccines in numerous clinical trials, but suffers from several inherent liabilities, including scarcity, chemical instability, and dose-limiting toxicity. Moreover, little is known about its mechanism of action. Over a decade-long effort, beginning at the University of Illinois at Urbana-Champaign and continuing at the Memorial Sloan Kettering Cancer Center (MSKCC), the group of Prof. David Y. Gin accomplished the total synthesis of QS-21 and developed a practical semisynthetic approach to novel variants that overcome the liabilities of the natural product. First, semisynthetic QS-21 variants were designed with stable amide linkages in the acyl chain domain that exhibited comparable in vivo adjuvant activity and lower toxicity than the natural product. Further modifications in the acyl chain domain and truncation of the linear tetrasaccharide domain led to identification of a trisaccharide variant with a simple carboxylic acid side chain that retained potent adjuvant activity, albeit with reemergence of toxicity. Conversely, an acyl chain analogue terminating in a free amine was inactive but enabled chemoselective functionalization with radiolabeled and fluorescent tags, yielding adjuvant-active saponin probes that, unlike inactive congeners, accumulated in the lymph nodes in vaccinated mice and internalized into dendritic cells. Subtle variations in length, stereochemistry, and conformational flexibility around the central glycosidic linkage provided QS-21 variants with adjuvant activities that correlated with specific conformations found in molecular dynamics simulations. Notably, deletion of the entire branched trisaccharide domain afforded potent, truncated saponin variants with negligible toxicity and improved synthetic access, facilitating subsequent investigation of the triterpene core. The triterpene C4-aldehyde substituent, previously proposed to be important for QS-21 adjuvant activity, proved to be dispensable in these truncated saponin variants, while the presence of the C16 hydroxyl group enhanced activity. Novel adjuvant conjugates incorporating the small-molecule immunopotentiator tucaresol at the acyl chain terminus afforded adjuvant-active variants but without significant synergistic enhancement of activity. Finally, a new divergent synthetic approach was developed to provide versatile and streamlined access to additional linear oligosaccharide domain variants with modified sugars and regiochemistries, opening the door to the rapid generation of diverse, synthetically accessible analogues. In this Account, we summarize these multidisciplinary studies at the interface of chemistry, immunology, and medicine, which have provided critical information on the structure–activity relationships (SAR) of this Quillaja saponin class; access to novel, potent, nontoxic adjuvants for use in subunit vaccines; and a powerful platform for investigations into the mechanisms of saponin immunopotentiation.

Progress and challenges associated with the development of ricin toxin subunit vaccines

The past several years have seen major advances in the development of a safe and efficacious ricin toxin vaccine, including the completion of two Phase I clinical trials with two different recombinant A subunit (RTA)-based vaccines: RiVax™ and RVEc™ adsorbed to aluminum salt adjuvant, as well as a non-human primate study demonstrating that parenteral immunization with RiVax elicits a serum antibody response that was sufficient to protect against a lethal dose aerosolized ricin exposure. One of the major obstacles moving forward is assessing vaccine efficacy in humans, when neither ricin-specific serum IgG endpoint titers nor toxin-neutralizing antibody levels are accepted as definitive predictors of protective immunity. In this review we summarize ongoing efforts to leverage recent advances in our understanding of RTA-antibody interactions at the structural level to develop novel assays to predict vaccine efficacy in humans.

Immunological evaluation of colonic delivered Hepatitis B surface antigen loaded TLR-4 agonist modified solid fat nanoparticles

Hepatitis B is one of the leading liver diseases and remains a major global health problem. Currently available vaccines provide protection but often results in weaker/minimal mucosal immunity. Thus the present study is devoted to the development and in-vivo exploration of the colonically delivered biomimetic nanoparticles which capably enhance humoral as well as cellular immune response. In present work, Hepatitis B surface antigen (HBsAg) entrapped nanoparticles containing Monophosphoryl lipid A (MPLA) (HB+L-NP) were prepared by solvent evaporation method and characterized for particle size (~210nm), shape, zeta potential (-24mV±0.68), entrapment efficiency (58.45±1.68%), in-vitro release and antigen integrity. Dose escalation study was done to confirm prophylactic immune response following defined doses of prepared nanoparticulate formulations with or without MPLA. Intramuscular administered alum based marketed HBsAg (Genevac B) was used as standard (10μg) and were able to induce significant systemic (IgG) but remarkably low mucosal immune (IgA) response. Notably, HB+L-NP (0.5ml-10μg) induced strong systemic and robust mucosal immunity (510 and 470 mIU/ml respectively, p<0.001) from which mucosal was more significant due to the involvement of Common Mucosal Immune System (CMIS). Likewise, significant cellular immune response was elicited by HB+L-NP through T-cell activation (mixed Th1 and Th2) as confirmed by significantly increased cytokines level (IL-2 and Interferon-γ) in spleen homogenates. This study supports that delivery of HBsAg to the colon may open new vista in designing oral vaccines later being one of most accepted route for potential vaccines in future.

Obesity Outweighs Protection Conferred by Adjuvanted Influenza Vaccination

Obesity is a risk factor for developing severe influenza virus infection, making vaccination of utmost importance for this high-risk population. However, vaccinated obese animals and adults have decreased neutralizing antibody responses. In these studies, we tested the hypothesis that the addition of either alum or a squalene-based adjuvant (AS03) to an influenza vaccine would improve neutralizing antibody responses and protect obese mice from challenge. Our studies demonstrate that adjuvanted vaccine does increase both neutralizing and nonneutralizing antibody levels compared to vaccine alone. Although obese mice mount significantly decreased virus-specific antibody responses, both the breadth and the magnitude of the responses against hemagglutinin (HA) and neuraminidase (NA) are decreased compared to the responses in lean mice. Importantly, even with a greater than fourfold increase in neutralizing antibody levels, obese mice are not protected against influenza virus challenge and viral loads remain elevated in the respiratory tract. Increasing the antigen dose affords no added protection, and a decreasing viral dose did not fully mitigate the increased mortality seen in obese mice. Overall, these studies highlight that, while the use of an adjuvant does improve seroconversion, vaccination does not fully protect obese mice from influenza virus challenge, possibly due to the increased sensitivity of obese animals to infection. Given the continued increase in the global obesity epidemic, our findings have important implications for public health.

Vaccination is the most effective strategy for preventing influenza virus infection and is a key component for pandemic preparedness. However, vaccines may fail to provide optimal protection in high-risk groups, including overweight and obese individuals. Given the worldwide obesity epidemic, it is imperative that we understand and improve vaccine efficacy. No work to date has investigated whether adjuvants increase the protective capacity of influenza vaccines in the obese host. In these studies, we show that adjuvants increased the neutralizing and nonneutralizing antibody responses during vaccination of lean and obese mice to levels considered “protective,” and yet, obese mice still succumbed to infection. This vulnerability is likely due to a combination of factors, including the increased susceptibility of obese animals to develop severe and even lethal disease when infected with very low viral titers. Our studies highlight the critical public health need to translate these findings and better understand vaccination in this increasing population.

Synthesis and immunostimulatory activity of substituted TLR7 agonists

Fifteen new substituted adenines were synthesized as potential TLR7 agonists. These compounds, along with 9 previously reported compounds, were analyzed for TLR7 activity and for the selective stimulation of B cell proliferation. Several functionalized derivatives exhibit significant activity, suggesting their potential for use as vaccine adjuvants.

Small-Molecule Carbohydrate-Based Immunostimulants

In this review, we discuss small-molecule, carbohydrate-based immunostimulants that target Toll-like receptor 4 (TLR-4) and cluster of differentiation 1D (CD1d) receptors. The design and use of these molecules in immunotherapy as well as results from their use in clinical trials are described. How these molecules work and their utilization as vaccine adjuvants are also discussed. Future applications and extensions for the use of these analogues as therapeutic agents will be outlined.

Influence of PapMV nanoparticles on the kinetics of the antibody response to flu vaccine

BACKGROUND

The addition of an adjuvant to a vaccine is a promising approach to increasing strength and immunogenicity towards antigens. Despite the fact that adjuvants have been used in vaccines for decades, their mechanisms of action and their influence on the kinetics of the immune response are still not very well understood. The use of papaya mosaic virus (PapMV) nanoparticles-a novel TLR7 agonist-was recently shown to improve and broaden the immune response directed to trivalent inactivated flu vaccine (TIV) in mice and ferrets.

RESULTS

We investigated the capacity of PapMV nanoparticles to increase the speed of the immune response toward TIV. PapMV nanoparticles induced a faster and stronger humoral response to TIV that was measured as early as 5 days post-immunization. The addition of PapMV nanoparticles was shown to speed up the differentiation of B-cells into early plasma cells, and increased the growth of germinal centers in a CD4+ dependent manner. TIV vaccination with PapMV nanoparticles as an adjuvant protected mice against a lethal infection as early as 10 days post-immunization.

CONCLUSION

In conclusion, PapMV nanoparticles are able to accelerate a broad humoral response to TIV. This property is of the utmost importance in the field of vaccination, especially in the case of pandemics, where populations need to be protected as soon as possible after vaccination.

Novel Ricin Subunit Antigens With Enhanced Capacity to Elicit Toxin-Neutralizing Antibody Responses in Mice

RiVax is a candidate ricin toxin subunit vaccine antigen that has proven to be safe in human phase I clinical trials. In this study, we introduced double and triple cavity-filling point mutations into the RiVax antigen with the expectation that stability-enhancing modifications would have a beneficial effect on overall immunogenicity of the recombinant proteins. We demonstrate that 2 RiVax triple mutant derivatives, RB (V81L/C171L/V204I) and RC (V81I/C171L/V204I), when adsorbed to aluminum salts adjuvant and tested in a mouse prime-boost-boost regimen were 5- to 10-fold more effective than RiVax at eliciting toxin-neutralizing serum IgG antibody titers. Increased toxin neutralizing antibody values and seroconversion rates were evident at different antigen dosages and within 7 days after the first booster. Quantitative stability/flexibility relationships analysis revealed that the RB and RC mutations affect rigidification of regions spanning residues 98-103, which constitutes a known immunodominant neutralizing B-cell epitope. A more detailed understanding of the immunogenic nature of RB and RC may provide insight into the fundamental relationship between local protein stability and antibody reactivity.