Preparation and characterisation of quillaja saponin with less heterogeneity than Quil-A

Structure Elucidation of Triterpenoid Saponins Found in an Immunoadjuvant Preparation of Quillaja brasiliensis Using Mass Spectrometry and 1H and 13C NMR Spectroscopy

An immunoadjuvant preparation (named Fraction B) was obtained from the aqueous extract of Quillaja brasiliensis leaves, and further fractionated by consecutive separations with silica flash MPLC and reverse phase HPLC. Two compounds were isolated, and their structures elucidated using a combination of NMR spectroscopy and mass spectrometry. One of these compounds is a previously undescribed triterpene saponin (Qb1), which is an isomer of QS-21, the unique adjuvant saponin employed in human vaccines. The other compound is a triterpene saponin previously isolated from Quillaja saponaria bark, known as S13. The structure of Qb1 consists of a quillaic acid residue substituted with a β-d-Galp-(1→2)-[β-d-Xylp-(1→3)]-β-d-GlcpA trisaccharide at C3, and a β-d-Xylp-(1→4)-α-l-Rhap-(1→2)-[α-l-Arap-(1→3)]-β-d-Fucp moiety at C28. The oligosaccharide at C28 was further substituted at O4 of the fucosyl residue with an acyl group capped with a β-d-Xylp residue.

The Phagosome-Lysosome Fusion Is the Target of a Purified Quillaja saponin Extract (PQSE) in Reducing Infection of Fish Macrophages by the Bacterial Pathogen Piscirickettsia salmonis

Piscirickettsia salmonis, the etiological agent of Piscirickettsiosis, is a Gram-negative and facultative intracellular pathogen that has affected the Chilean salmon industry since 1989. The bacterium is highly aggressive and can survive and replicate within fish macrophages using the Dot/Icm secretion system to evade the host’s immune response and spread systemically. To date, no efficient control measures have been developed for this disease; therefore, the producers use large amounts of antibiotics to control this pathogen. In this frame, this work has focused on evaluating the use of saponins from Quillaja saponaria as a new alternative to control the Piscirickettsiosis. It has been previously reported that purified extract of Q. saponaria (PQSE) displays both antimicrobial activity against pathogenic bacteria and viruses and adjuvant properties. Our results show that PQSE does not present antimicrobial activity against P. salmonis, although it reduces P. salmonis infection in an in vitro model, promoting the phagosome–lysosome fusion. Additionally, we demonstrate that PQSE modulates the expression of IL-12 and IL-10 in infected cells, promoting the immune response against the pathogen and reducing the expression of pathogen virulence genes. These results together strongly argue for specific anti-invasion and anti-intracellular replication effects induced by the PQSE in macrophages.

Replacing the Rhamnose-Xylose Moiety of QS-21 with Simpler Terminal Disaccharide Units Attenuates Adjuvant Activity in Truncated Saponin Variants

Adjuvants are key immunostimulatory components in vaccine formulations, which improve the immune response to the co-administered antigen. The saponin natural product QS-21 is one of the most promising immunoadjuvants in the development of vaccines against cancer and infectious diseases but suffers from limitations that have hampered its widespread human use. Previous structure-activity relationship studies have identified simplified saponin variants with truncated carbohydrate chains, but have not focused on the influence of the linear oligosaccharide domain of QS-21 in adjuvant activity. Herein, an expeditious 15-step synthesis of new linear trisaccharide variants of simplified QS-21-derived adjuvants is reported, in which the complex terminal xylose-rhamnose moiety has been replaced with commercially available, simpler lactose and cellobiose disaccharides in a β-anomeric configuration. In vivo immunological evaluation of the synthetic saponins showed attenuated antibody responses, highlighting the negative impact of such carbohydrate modifications on adjuvant activity, which could be associated with higher saponin conformational flexibility.

Natural and Synthetic Saponins as Vaccine Adjuvants

Saponin adjuvants have been extensively studied for their use in veterinary and human vaccines. Among them, QS-21 stands out owing to its unique profile of immunostimulating activity, inducing a balanced Th1/Th2 immunity, which is valuable to a broad scope of applications in combating various microbial pathogens, cancers, and other diseases. It has recently been approved for use in human vaccines as a key component of combination adjuvants, e.g., AS01b in Shingrix^® for herpes zoster. Despite its usefulness in research and clinic, the cellular and molecular mechanisms of QS-21 and other saponin adjuvants are poorly understood. Extensive efforts have been devoted to studies for understanding the mechanisms of QS-21 in different formulations and in different combinations with other adjuvants, and to medicinal chemistry studies for gaining mechanistic insights and development of practical alternatives to QS-21 that can circumvent its inherent drawbacks. In this review, we briefly summarize the current understandings of the mechanism underlying QS-21’s adjuvanticity and the encouraging results from recent structure-activity-relationship (SAR) studies.

Carbohydrate Immune Adjuvants in Subunit Vaccines

Modern subunit vaccines are composed of antigens and a delivery system and/or adjuvant (immune stimulator) that triggers the desired immune responses. Adjuvants mimic pathogen-associated molecular patterns (PAMPs) that are typically associated with infections. Carbohydrates displayed on the surface of pathogens are often recognized as PAMPs by receptors on antigen-presenting cells (APCs). Consequently, carbohydrates and their analogues have been used as adjuvants and delivery systems to promote antigen transport to APCs. Carbohydrates are biocompatible, usually nontoxic, biodegradable, and some are mucoadhesive. As such, carbohydrates and their derivatives have been intensively explored for the development of new adjuvants. This review assesses the immunological functions of carbohydrate ligands and their ability to enhance systemic and mucosal immune responses against co-administered antigens. The role of carbohydrate-based adjuvants/delivery systems in the development of subunit vaccines is discussed in detail.

Structural Effect on Adjuvanticity of Saponins

We have prepared a number of saponin-based vaccine adjuvant candidates. These unnatural saponins have a different terminal-functionalized side chain incorporated into the glucuronic acid unit that is attached to a triterpenoid core at its C3 position. The semisynthetic saponin adjuvants have shown significantly different immunostimulatory activities, suggesting that the structure of the side chain, triterpenoid core, and oligosaccharide domain together orchestrate saponin adjuvant's potentiation of immune responses. Among these new adjuvant candidates, VSA-2 (5b), a derivative of Momordica saponin (MS) II, showed consistent enhancement of immunoglobulin G2a (IgG2a) production when it was in formulation with either ovalbumin or recombinant hemagglutinin B (rHagB) antigen. With rHagB antigen, it induced a significantly higher IgG2a response than the positive control GPI-0100, a well-studied semisynthetic saponin adjuvant mixture derived from Quillaja saponaria Molina saponins, known for its ability to induce a balanced Th1/Th2 immunity. These results confirm that Momordica saponins are a viable natural source to provide potent saponin adjuvants after simple chemical derivatization and identify VSA-2 (5b) as another MS-based promising immunostimulant lead owing to its distinctive ability in potentiating the IgG2a response.

Vaccine Adjuvants Derivatized from Momordica Saponins I and II

We have derivatized Momordica saponins (MS) I and II through their coupling at C3 glucuronic acid site with dodecylamine. The derivatives show significantly different immunostimulant activity profiles from their respective natural parent saponins. In particular, adjuvant VSA-1 (5), the derivative of MS I, potentiates a significantly higher IgG2a responose than the corresponding natural product. Its IgG1 and IgG2a production is similar to that of GPI-0100, indicating a potential mixed and antigen-specific Th1/Th2 immune response, which is different from the Th2 immunity induced by the natural saponin MS I. In addition, toxicity evaluations show that adjuvant VSA-1 (5) is much less toxic than the widely used natural saponin mixture Quil A. These results prove that derivatizing Momordica saponins can be a viable way for easy access to structurally defined saponin immunostimulants with favorable adjvuant activity and low toxicity.

Phosphorylated Radix Cyathulae officinalis Polysaccharides Act as Adjuvant via Promoting Dendritic Cell Maturation

The aim of this study was to investigate whether phosphorylated Radix Cyathulae officinalis Kuan polysaccharides (pRCPS) used as adjuvant with foot-and-mouth disease vaccine (FMDV) can stimulate specific humoral and cellular immune responses in ICR mice. The results demonstrated that pRCPS significantly up-regulated FMDV-specific IgG, IgG1, IgG2b and IgG2a antibody levels and splenocyte proliferation. pRCPS also promoted the killing activities of cytotoxic T lymphocytes (CTL) and natural killer cells (NK). In addition, pRCPS enhanced the expression levels of IL-2, IL-4, and IFN-γ in CD4⁺ T cells and the level of IFN-γ in CD8⁺ T cells. Importantly, pRCPS enhanced the expression of MHCII, CD40⁺, CD86⁺, and CD80⁺ in dendritic cells (DCs). This study indicated that phosphorylation modification could increase immune-enhancing activities of RCPS, and pRCPS could promote humoral and cellular immune responses through facilitating DC maturation.

The Adjuvant Activity of Epimedium Polysaccharide-Propolis Flavone Liposome on Enhancing Immune Responses to Inactivated Porcine Circovirus Vaccine in Mice

Objectives. The adjuvant activity of Epimedium polysaccharide-propolis flavone liposome (EPL) was investigated in vitro and in vivo. Methods. In vitro, the effects of EPL at different concentrations on splenic lymphocytes proliferation and mRNA expression of IFN-γ and IL-6 were determined. In vivo, the adjuvant activities of EPL, EP, and mineral oil were compared in BALB/c mice through vaccination with inactivated porcine circovirus type 2 (PCV2) vaccine. Results. In vitro, EPL promoted lymphocytes proliferation and increased the mRNA expression of IFN-γ and IL-6, and the effect was significantly better than EP at all concentrations. In vivo, EPL significantly promoted the lymphocytes proliferation and the secretion of cytokines and improved the killing activity of NK cells, PCV2-specific antibody titers, and the proportion of T-cell subgroups. The effects of EPL were significantly better than EP and oil adjuvant at most time points. Conclusion. EPL could significantly improve both PCV2-specific cellular and humoral immune responses, and its medium dose had the best efficacy. Therefore, EPL would be exploited in an effective immune adjuvant for inactivated PCV2 vaccine.

Versatile strategy for the divergent synthesis of linear oligosaccharide domain variants of Quillaja saponin vaccine adjuvants

We describe a new, versatile synthetic approach to Quillaja saponin variants based on the natural product immunoadjuvant QS-21. This modular, divergent strategy provides efficient access to linear oligosaccharide domain variants with modified sugars and regiochemistries. This new synthetic approach opens the door to the rapid generation of diverse analogues to identify novel saponin adjuvants with improved synthetic accessibility.

Design, synthesis, and immunologic evaluation of vaccine adjuvant conjugates based on QS-21 and tucaresol

Immunoadjuvants are used to potentiate the activity of modern subunit vaccines that are based on molecular antigens. An emerging approach involves the combination of multiple adjuvants in a single formulation to achieve optimal vaccine efficacy. Herein, to investigate such potential synergies, we synthesized novel adjuvant conjugates based on the saponin natural product QS-21 and the aldehyde tucaresol via chemoselective acylation of an amine at the terminus of the acyl chain domain in QS saponin variants. In a preclinical mouse vaccination model, these QS saponin-tucaresol conjugates induced antibody responses similar to or slightly higher than those generated with related QS saponin variants lacking the tucaresol motif. The conjugates retained potent adjuvant activity, low toxicity, and improved activity-toxicity profiles relative to QS-21 itself and induced IgG subclass profiles similar to those of QS-21, indicative of both Th1 cellular and Th2 humoral immune responses. This study opens the door to installation of other substituents at the terminus of the acyl chain domain to develop additional QS saponin conjugates with desirable immunologic properties.

Variation of Saponin Contents and Physiological Status in Quillaja saponaria Under Different Environmental Conditions

Quillaja saponaria (Quillay), an evergreen tree found in Chile, is one of the main sources of saponins. Quillaja saponins have hypocholesterolaemic, anticarcinogenic, antioxidant and pesticidal properties, and are used as adjuvants for vaccines. Samples of Quillay growing at three zones in O'Higgins Region, Chile (Coastal, Central and Mountain zones) were analyzed for content of saponins and physiological status. The results revealed differences in the content of saponins depending on the zone of sample collection. The highest contents were found in samples from the Mountain zone, where the highest saponin contents were accompanied by the lowest foliar nitrogen contents, the highest antioxidant activity and the highest carotenoid contents. The results suggest a physiological and adaptive mechanism of saponins in plants to survive under unfavourable environmental conditions. The results have important implications for a theoretical basis for the design of a reasonable harvest, to avoid the cost of poor quality material, and also to provide a sustainable use and conservation of this important species. Further research on the effects of stress will improve our understanding of the saponins production and their physiological functions in plants, whereas they have generally been studied for their biological and chemical applications.

Enhancing Immunogenicity of Cancer Vaccines: QS-21 as an Immune Adjuvant

Saponins comprise a class of plant natural products that incorporate a lipophilic terpenoid core, to which is appended one or more carbohydrate residues. They are amphiphilic molecules and often exhibit toxic biological profiles, likely as a result of their roles as vital components in protective coatings to defend against phytopathogen infection and insect predation. The most notable of adjuvant-active saponins investigated for vaccine development come from the Chilean Soapbark Tree, Quillaja saponaria (i.e., QS). More than 30 years ago, semi-purified extracts (i.e., Quil A) from the cortex of Quillaja saponaria were found to be highly effective as adjuvants in veterinary vaccines. However, due to significant and variable toxicity effects, Quil A was not deemed appropriate for human vaccines. More refined purification methods have led to multiple fractions which are derived from the original plant extract. As such, QS-21 to date appears to be one of the more scientifically interesting and robust adjuvants in use in vaccinology. The role of QS-21 as an adjuvant for use in a variety of cancer vaccine trials and its comparison to other adjuvants is discussed in this review.

Natural and synthetic saponin adjuvant QS-21 for vaccines against cancer

One of the most widely used and potent immunological adjuvants is a mixture of soluble triterpene glycosides purified from the soap bark tree (Quillaja saponaria). Despite challenges in production, quality control, stability and toxicity, the QS-21 fraction from this extract has exhibited exceptional adjuvant properties for a range of antigens. It possesses an ability to augment clinically significant antibody and T-cell responses to vaccine antigens against a variety of infectious diseases, degenerative disorders and cancers. The recent synthesis of active molecules of QS-21 has provided a robust method to produce this leading vaccine adjuvant in high purity as well as to produce novel synthetic QS-21 congeners designed to induce increased immune responsiveness and decreased toxicity.

Design and synthesis of potent Quillaja saponin vaccine adjuvants

The success of antitumor and antiviral vaccines often requires the use of an adjuvant, a substance that significantly enhances the immune response to a coadministered antigen. Only a handful of adjuvants have both sufficient potency and acceptable toxicity for clinical investigation. One promising adjuvant is QS-21, a saponin natural product that is the immunopotentiator of choice in many cancer and infectious disease vaccine clinical trials. However, the therapeutic promise of QS-21 adjuvant is curtailed by several factors, including its scarcity, difficulty in purification to homogeneity, dose-limiting toxicity, and chemical instability. Here, we report the design, synthesis, and evaluation of chemically stable synthetic saponins. These novel, amide-modified, non-natural substances exhibit immunopotentiating effects in vivo that rival or exceed that of QS-21 in evaluations with the GD3-KLH melanoma conjugate vaccine. The highly convergent synthetic preparation of these novel saponins establishes new avenues for discovering improved molecular adjuvants for specifically tailored vaccine therapies.

Evaluation of ISCOM-adjuvanted subunit vaccines containing recombinant feline immunodeficiency virus Rev, OrfA and envelope protein in cats

For the development of feline immunodeficiency virus (FIV) vaccines mostly structural proteins have been evaluated for their capacity to induce protective immunity. In the present study, subunit vaccines containing recombinant FIV accessory proteins Rev and OrfA were evaluated in cats. Cats were vaccinated repeatedly with these proteins, adjuvanted with immune stimulating complexes (ISCOMs). In addition, cats were vaccinated with bacterially expressed fragments spanning the entire FIV envelope protein, either alone or in combination with the regulatory proteins. Subsequently, the cats were challenged with a homologous FIV strain to assess the level of protective immunity achieved with the respective vaccination regimens. Although the vaccines proved to be immunogenic, vaccinated cats were not protected from infection with FIV.

Immune response in rhesus macaques after mixed modality immunisations with DNA, recombinant adenovirus and recombinant gp120 from human immunodeficiency virus type 1

The establishment of effective regimens for a vaccine against human immunodeficiency virus type 1 (HIV-1) is urgently needed. In the present study we have produced HIV-1 gp120 from a vaccine-relevant primary R5 isolate in recombinant vaccinia (rVV)-infected Vero cells. We have investigated the effect of boosting with this protein in mixed modality immunisations of rhesus macaques following different immunisation. As reported earlier, animals were primed with codon-optimised HIV-1(BX08)env DNA delivered as plasmid or as replication-deficient recombinant human adenovirus type 5 (rAd5), which both induced specific antibody and cellular immune responses (1). Boosting with rAd5 temporarily had increased the anti-gp120 antibody titres approximately 1 log (rAd5+rAd5) or 3 log (DNA+rAd5) (1). However, secondary rAd5 boosting showed less effect due to the induced vector-specific immunity. To further boost the antibody response, the rgp120(BX08) was injected with Quadri A saponin adjuvant. The protein boosting resulted in a 1-2 log antibody increase and also boosting of the cell-mediated immune response. Neutralising antibodies to the heterologous HIV-1(MN) were detected; however, neutralising antibodies to the primary HIV-1(Bx08) isolate were seen only transiently after rAd5 but not the rgp120 immunisation. It is concluded that the rgp120(Bx08) reagent from rVV-infected Vero cells is functional and immunogenic in macaques, inducing both antibody and cellular immunity. The rgp120(Bx08) is a relevant model antigen that may be used to boost antibody and cellular immunity in mixed modality vaccine regimens against HIV-1 in higher animals.

The combined CTA1-DD/ISCOMs vector is an effective intranasal adjuvant for boosting prior Mycobacterium bovis BCG immunity to Mycobacterium tuberculosis

Infection with Mycobacterium tuberculosis, the causative agent of tuberculosis (TB), remains one of the leading causes of mortality worldwide. The current "gold standard" vaccine Mycobacterium bovis BCG has a limited efficacy that wanes over time. The development of a vaccine to boost BCG-induced immunity is therefore a highly active area of research. Mucosal administration of vaccines is believed to provide better protection against pathogens, such as M. tuberculosis, that invade the host via mucosal surfaces. In this study we demonstrate that an intranasal vaccine, comprising the antigenic fusion protein Ag85B-ESAT-6 and the mucosal combined adjuvant vector CTA1-DD/ISCOMs, strongly promotes a Th1-specific immune response, dominated by gamma interferon-secreting CD4-positive T cells. Mucosal administration of Ag85B-ESAT-6 mixed with CTA1-DD/ISCOMs strongly boosted prior BCG immunity, leading to a highly increased recruitment of antigen-specific cells to the site of infection. Most importantly, we observed a significantly (P < 0.001) reduced bacterial burden in the lung compared to nonboosted control animals. Thus, the results demonstrate the effectiveness of mucosal vaccination with Ag85B-ESAT-6 mixed with CTA1-DD/ISCOMs as adjuvant for stimulating TB-specific protective immunity in the lung.

Immunogenicity of Liposomes Containing Lipid Core Peptides and the Adjuvant Quil A

PURPOSE

The purpose of this study was to investigate the immunogenicity of liposomes containing mannosylated lipid core peptide (manLCP) constructs, both in vitro and in vivo, with or without the addition of the immune stimulating adjuvant Quil A.

METHODS

Mouse bone marrow dendritic cells (BMDC) were cultured with liposome formulations for 48 h, and the resulting level of BMDC activation was determined by flow cytometry. BMDC pulsed with liposome formulations were incubated with 5,6-carboxyfluoroscein diacetate succinimidyl ester-labeled T cells for 72 h and the resulting T cell proliferation was determined by flow cytometry. To investigate the immunogenicity of formulations in vivo, groups of C57Bl/6J mice were immunized by subcutaneous injection, and the resulting antigen-specific cytotoxic and protective immune responses toward tumor challenge evaluated.

RESULTS

Despite being unable to demonstrate the activation of BMDC, BMDC pulsed with liposomes containing manLCP constructs were able to stimulate the proliferation of naïve T cells in vitro. However, in vivo only liposomes containing both manLCP and Quil A were able to stimulate a strong antigen-specific cytotoxic immune response. Liposomes containing manLCP and Quil A within the same particle were able to protect against the growth of tumor cells to a similar level as if the antigen was administered in alum with CD4 help.

CONCLUSION

ManLCPs administered in liposomes are able to stimulate strong cytotoxic and protective immune responses if Quil A is also incorporated as an adjuvant.

Immunogenicity in Mamu-A*01 rhesus macaques of a CCR5-tropic human immunodeficiency virus type 1 envelope from the primary isolate (Bx08) after synthetic DNA prime and recombinant adenovirus 5 boost

Envelopes of primary R5-tropic human immunodeficiency virus type 1 (HIV-1) isolates may be particularly relevant for vaccine purposes and should be evaluated for immunogenicity in animals including macaques before carrying out human vaccine trials. In the present study, the immunogenicities of synthetic HIV-1 env DNA vaccines, which had been derived from the early primary isolate Bx08 and contain humanized codons, were evaluated in mice, guinea pigs and rhesus macaques. Neutralization sensitivity of the HIV-1(Bx08) isolate was found to resemble that of other primary isolate prototypes. Immunogenicity of gp120 delivered as codon-optimized DNA vaccine was comparable to that of recombinant gp120 protein plus adjuvant in mice. Similarly, DNA vaccination of guinea pigs with synthetic gp140(Bx08) and gp150(Bx08) DNA induced a strong antibody response independent of the gene construct and DNA immunization route. Mamu-A*01 rhesus macaques were DNA vaccinated with synthetic gp150(Bx08) or gp140(Bx08) DNA and boosted with a replication-deficient recombinant human adenovirus type 5 expressing a synthetic gp120(Bx08) gene. DNA-vaccinated rhesus macaques developed specific CD8+ T lymphocyte responses and anti-rgp120(IIIb) antibody responses. Both the humoral and cellular responses were significantly improved following intramuscular boosting with the recombinant adenovirus. The demonstrated humoral and cellular immunogenicities of these HIV Bx08 Env vaccines in non-human primates encourages their further development as one component in candidate HIV vaccines for humans.

Longevity of neutralizing antibody levels in macaques vaccinated with Quil A-adjuvanted measles vaccine candidates

Quil A-based candidate measles vaccines have been shown to be immunogenic and protective in cotton rats and macaques. Here we studied the longevity of protective VN antibody levels induced in macaques with one dose of measles virus (MV) iscom. Inactivated MV adjuvanted with iscom-matrix or with purified Quillaja saponin QA-22 were also tested. All animals developed high levels of VN antibody and MV-specific IFNgamma-producing cells. Especially the high VN antibody levels induced by the latter two preparations showed virtually no decrease during the 2-year follow-up. These highly promising candidate MV vaccines should now be tested in infant macaques in the presence or absence of passively transferred and/or maternally derived VN antibodies. In addition, the immunopathological safety of the constructs should be evaluated in the atypical measles model in rhesus macaques.

CTA1-DD-immune stimulating complexes: a novel, rationally designed combined mucosal vaccine adjuvant effective with nanogram doses of antigen

Mucosally active vaccine adjuvants that will prime a full range of local and systemic immune responses against defined antigenic epitopes are much needed. Cholera toxin and lipophilic immune stimulating complexes (ISCOMS) containing Quil A can both act as adjuvants for orally administered Ags, possibly by targeting different APCs. Recently, we have been successful in separating the adjuvant and toxic effects of cholera toxin by constructing a gene fusion protein, CTA1-DD, that combines the enzymatically active CTA1-subunit with a B cell-targeting moiety, D, derived from Staphylococcus aureus protein A. Here we have extended this work by combining CTA1-DD with ISCOMS, which normally target dendritic cells and/or macrophages. ISCOMS containing a fusion protein comprising the OVA(323-339) peptide epitope linked to CTA1-DD were highly immunogenic when given in nanogram doses by the s.c., oral, or nasal routes, inducing a wide range of T cell-dependent immune responses. In contrast, ISCOMS containing the enzymatically inactive CTA1-R7K-DD mutant protein were much less effective, indicating that at least part of the activity of the combined vector requires the ADP-ribosylating property of CTA1. No toxicity was observed by any route. To our knowledge, this is the first report on the successful combination of two mechanistically different principles of adjuvant action. We conclude that rationally designed vectors consisting of CTA1-DD and ISCOMS may provide a novel strategy for the generation of potent and safe mucosal vaccines.