Sulfolipo-cyclodextrin in squalane-in-water as a novel and safe vaccine adjuvant

Carbohydrate fatty acid monosulphate ester is a potent adjuvant for low-dose seasonal influenza vaccines

There is still a need for a better and affordable seasonal influenza vaccine and the use of an adjuvant could solve both issues. Therefore, immunogenicity of a combination of low dose of 1/5TH (3 µg of HA) a licensed seasonal flu vaccine with the novel carbohydrate fatty acid monosulfate ester (CMS)-based adjuvant was investigated in ferrets and safety in rabbits. Without CMS, hemagglutination inhibition (HI) antibody titers ranged from ≤5 to 26 three weeks post immunization 1 (PV-1) and from 7 to 134 post-immunization 2 (PV-2) in ferrets. Virus neutralizing (VN) antibody titers ranged from 20 to 37 PV-1 and from 21 to 148 PV-2. CMS caused 10 to 111- fold increase in HI titers and 3 to 58- fold increase in VN titers PV-1 and PV-2, depending on influenza strain and dose of adjuvant. Eight mg of CMS generated significantly higher antibody titers than 1 or 4 mg, while 1 and 4 mg induced similar responses. Three µg of HA plus 4 mg of CMS was considered the highest human dose and safety of two-fold this dose was determined in acute and repeated-dose toxicity studies in rabbits conducted according to OECD GLP guidelines. The test item did not elicit any clinical signs, local reactions, effect on body weight, effect on urine parameters, effect on blood biochemistry, or gross pathological changes. In blood, increased numbers of neutrophils, lymphocytes and/or monocytes were noted and in iliac lymph nodes, increased cellularity of macrophages of minimal to mild degree were observed. In both ferrets and rabbits, body temperature increased with increasing dose of CMS to a maximum of 1 ˚C during the first day post-immunization, which returned to normal values during the second day. In the local tolerance study, histopathology of the site of injection at 7 days PV-1 revealed minimal, mild or moderate inflammation in 5, 8 and 5 animals, respectively. In the repeated-dose study and 21 days PV-3, minimal, mild or moderate inflammation was observed in 15, 18 and 3 animals, respectively. We concluded that the data show CMS is a potent and safe adjuvant ready for further clinical development of a seasonal influenza vaccine and combines high immunogenicity with possible antigen-sparing capacity.

Adjuvants Differentially Modulate the Immunogenicity of Lassa Virus Glycoprotein Subunits in Mice

Lassa Fever (LF) is an acute viral hemorrhagic fever caused by Lassa virus (LASV) that is primarily transmitted through contact with wild rodents in West Africa. Although several advanced vaccine candidates are progressing through clinical trials, some effective vaccines are virally vectored and thus require a stringent cold-chain, making distribution to rural and resource-poor areas difficult. Recombinant subunit vaccines are advantageous in this aspect as they can be thermostabilized and deployed with minimal storage and transportation requirements. However, antigen dose and adjuvant formulation must be carefully selected to ensure both the appropriate humoral and cell-mediated immune responses are elicited. In this study, we examine the immunogenicity of a two-step immunoaffinity-purified recombinant LASV glycoprotein (GP) with five clinical- and preclinical-grade adjuvants. Swiss Webster mice immunized intramuscularly with 2 or 3 doses of each vaccine formulation showed complete seroconversion and maximal GP-specific antibody response after two immunizations. Formulations with GPI-0100, LiteVax, Montanide™ ISA 51, and Montanide™ ISA 720 induced both IgG1 and IgG2 antibodies suggesting a balanced Th1/Th2 response, whereas formulation of LASV GP with Alhydrogel elicited a IgG1-dominant response. Splenocytes secreting both Th1 and Th2 cytokines i.e., IFN-γ, TNF-α, IL-2, IL-4 and IL-5, were observed from mice receiving both antigen doses formulated with ISA 720, LiteVax and GPI-0100. However, robust, multifunctional T-cells were only detected in mice receiving a higher dose of LASV GP formulated with GPI-0100. Our results emphasize the importance of careful adjuvant selection and lay the immunological basis for a recombinant subunit protein LF vaccine formulation.

Cyclodextrins in Antiviral Therapeutics and Vaccines

The present review describes the various roles of cyclodextrins (CDs) in vaccines against viruses and in antiviral therapeutics. The first section describes the most commonly studied application of cyclodextrins—solubilisation and stabilisation of antiviral drugs; some examples also refer to their beneficial taste-masking activity. The second part of the review describes the role of cyclodextrins in antiviral vaccine development and stabilisation, where they are employed as adjuvants and cryopreserving agents. In addition, cyclodextrin-based polymers as delivery systems for mRNA are currently under development. Lastly, the use of cyclodextrins as pharmaceutical active ingredients for the treatment of viral infections is explored. This new field of application is still taking its first steps. Nevertheless, promising results from the use of cyclodextrins as agents to treat other pathologies are encouraging. We present potential applications of the results reported in the literature and highlight the products that are already available on the market.

Carbohydrate fatty acid monosulphate esters are safe and effective adjuvants for humoral responses

Carbohydrate fatty acid sulphate esters (CFASEs) formulated in a squalane-in-water emulsion are effective adjuvants for humoral responses to a wide range of antigens in various animal species but rise in body temperature and local reactions albeit mild or minimal hampers application in humans. In rabbits, body temperature increased 1°C one day after intramuscular (IM) injection, which returned to normal during the next day. The effect increased with increasing dose of CFASE but not with the number of injections (up to 5). Antigen enhanced the rise in body temperature after booster immunization (P<0.01) but not after priming. Synthetic CFASEs are mixtures of derivatives containing no sulphate, one or multiple sulphate groups and the monosulphate derivatives (CMS) were isolated, incorporated in a squalane in-water emulsion and investigated. In contrast to CFASE, CMS adjuvant did not generate rise in body temperature or local reactions in rabbits immunized with a purified, recombinant malaria chimeric antigen R0.10C. In comparison to alum, CMS adjuvant revealed approximately 30-fold higher antibody titres after the first and >100-fold after the second immunization. In ferrets immunized with 7.5μg of inactivated influenza virus A/H7N9, CMS adjuvant gave 100-fold increase in HAI antibody titres after the first and 25-fold after the second immunisation, which were 10-20-fold higher than with the MF59-like AddaVax adjuvant. In both models, a single immunisation with CMS adjuvant revealed similar or higher titres than two immunisations with either benchmark, without detectable systemic and local adverse effects. Despite striking chemical similarities with monophospholipid A (MPL), CMS adjuvant did not activate human TLR4 expressed on HEK cells. We concluded that the synthetic CMS adjuvant is a promising candidate for poor immunogens and single-shot vaccines and that rise in body temperature, local reactions or activation of TLR4 is not a pre-requisite for high adjuvanticity.

Large-animal model for establishing E/T ratio of adjuvants

To develop novel adjuvants for use in humans, the efficacy/toxicity (E/T) ratio of experimental products in large animal species can be investigated. The test model included two intramuscular immunizations in pigs at 3 weeks interval and analysis of immune responses and local reactions 1 week after the second injection. The antigen used to determine adjuvant activity was a well-defined, purified, viral glycoprotein that without adjuvant induces low immune responses and no detectable local reactions. Efficacy was determined by measuring ELISA and virus-neutralizing antibody titres. Toxicity was determined by necropsy and estimating size and severity of local reactions to each treatment. The persistence of the side effects was deduced from the difference in the local reaction 4 weeks after the first and 1 week after the second injection. For graphic representation of E/T ratios, toxicity was expressed in arbitrary units and plotted against antibody titre. The graphs provided insight into dose- and structure-response relationships and enabled the stepwise optimization of adjuvant candidates.

Squalene: A natural triterpene for use in disease management and therapy

Squalene is a natural lipid belonging to the terpenoid family and a precursor of cholesterol biosynthesis. It is synthesized in humans and also in a wide array of organisms and substances, from sharks to olives and even bran, among others. Because of its significant dietary benefits, biocompatibility, inertness, and other advantageous properties, squalene is extensively used as an excipient in pharmaceutical formulations for disease management and therapy. In addition, squalene acts as a protective agent and has been shown to decrease chemotherapy-induced side-effects. Moreover, squalene alone exhibits chemopreventive activity. Although it is a weak inhibitor of tumor cell proliferation, it contributes either directly or indirectly to the treatment of cancer due to its potentiation effect. In addition, squalene enhances the immune response to various associated antigens, and it is therefore being investigated for vaccine delivery applications. Since this triterpene is well absorbed orally, it has been used to improve the oral delivery of therapeutic molecules. All of these qualities have rendered squalene a potentially interesting excipient for pharmaceutical applications, especially for the delivery of vaccines, drugs, genes, and other biological substances. This paper is the first review of its kind and offers greater insight into squalene's direct or indirect contribution to disease management and therapy.

Squalene emulsions for parenteral vaccine and drug delivery

Squalene is a linear triterpene that is extensively utilized as a principal component of parenteral emulsions for drug and vaccine delivery. In this review, the chemical structure and sources of squalene are presented. Moreover, the physicochemical and biological properties of squalene-containing emulsions are evaluated in the context of parenteral formulations. Historical and current parenteral emulsion products containing squalene or squalane are discussed. The safety of squalene-based products is also addressed. Finally, analytical techniques for characterization of squalene emulsions are examined.

Preparation and Evaluation of Multiple Emulsions Water-in-oil-in-water (w/o/w) as Delivery System for Influenza Virus Antigens

In this study, investigations have been carried out to prepare adjuvant active delivery systems; multiple water-in-oil-in-water (w/o/w) emulsion formulations, containing influenza virus surface antigen Hemagglutinin (HA). A modified two-stage emulsification method has been used to prepare multiple emulsions. After improving multiple (w/o/w) emulsion formulations; F1: purified antigen solution (PAS)/soybean oil, HCO-40 and span 80/pluronic F-68, F2: PAS and HPbetaCD/soybean oil, HCO-40 and span 80/pluronic F-68, F3: PAS/squalane, HCO-40 and span 80/pluronic F-68, formulations were selected for the stability study that continued for a 3 month duration. To evaluate the stability of these formulations, microscopic observation, osmolarities of the internal and external aqueous phases, pH, globule size and viscosity were determined. SDS-PAGE (silver staining) was used to evaluate HA and the micro-bicinchoninic acid (mBCA) assay was used to determine the in vitro release of antigen from formulations. Immune responses of formulations were investigated in Wistar Albino rats and compared with the immune response raised against the conventional vaccine. These responses were detected with Hemagglutination Inhibition (HAI) assay. The results of this study demonstrated that HA was well entrapped in the multiple (w/o/w) emulsion formulations. Molecular weight and antigenicity of the entrapped HA were not affected by the emulsification procedure. These results suggest that multiple emulsion formulations entrapping influenza antigen may have potential for immunization studies as one of the vaccine delivery system with adjuvant properties.

A novel recombinant virus-like particle vaccine for prevention of porcine parvovirus-induced reproductive failure

A novel vaccine against porcine parvovirus (PPV), composed of recombinant virus-like particles (PPV-VLPs) produced with the baculovirus expression vector system (BEVS) at industrial scale, was tested for its immunogenicity and protective potency. A formulation of submicrogram amounts of PPV-VLPs in a water-in-mineral oil adjuvant evoked high serum antibody titres in both guinea pigs, used as reference model, and target species, pigs. A single immunisation with 0.7microg of this antigen yielded complete foetal protection against PPV infection after challenge with a virulent strain of this virus. Furthermore, also in the presence of mild adjuvants the protective action of these PPV-VLPs is excellent. This recombinant subunit vaccine overcomes some of the drawbacks of classical PPV vaccines.

Experimental squalene adjuvant

The authors prepared experimental lipoid adjuvant of the oil-in-water (O/W) type, based on squalene (ESA: experimental squalene adjuvant), intended for liquid inactivated veterinary vaccines. The final concentration of squalene in the vaccine was 5% (w/v). Detergents Poloxamer 105 in the concentration of 4% (w/v) and Abil-Care in the concentration of 2% were used as emulsifiers. The water component was inactivated virus suspension. Emulsification at decreased temperatures (up to 37 degrees C) fails to denaturate the immunization antigen. The effectiveness of experimental squalene adjuvant was tested using a liquid inactivated adjuvant rabies vaccine and a liquid porcine parvovirus vaccine in comparison with adjuvant-free vaccines or vaccines potentiated with aluminium hydroxide. The squalene adjuvant increased the immunogenic activity of non-potentiated rabies vaccine approximately 1.8-fold, while aluminium hydroxide increased the effectiveness of rabies vaccine only 1.08-fold. The antigenic activity, i.e. the level of specific antibodies after vaccination was significantly increased by using both adjuvants; ESA was more efficient than aluminium hydroxide.

Separation and characterization of adjuvant oligosaccharide oleate ester derived from product mixture of mannitol-oleic acid esterification

Nearly 30 years after intense investigations of mannide monooleates for use as vaccine adjuvants, a novel adjuvant-active saccharide oleate ester was isolated and identified from the product mixture synthesized from mannitol and oleic acid. The mixture, which contained many kinds of mannide mono- and dioleates and their derivatives, was fractionated by liquid chromatography (LC), and the fraction with the highest adjuvanticity was obtained. Gel permeation chromatography (GPC) showed that it consisted of one major compound with an average molecular weight (MW) 2850. Infrared (IR) absorption and proton nuclear magnetic resonance spectra suggested it had oligosaccharide moieties and oleate domains. These findings suggested that it was an oligosaccharide oleate ester of the average MW 2850. The molecular ratio of oleate chains per monosaccharide unit was approximately 0.8. The ester induced both IgG1 and IgG2a antibody responses in mice in a dispersed form without base oil. This ester thus appears to be one of the adjuvant-active compounds largely contributing to the excellent adjuvanticity of mannide oleate mixture broadly used as vaccine emulsifier. These results and previous findings suggest that the fundamental adjuvanticity of this 'oligo' saccharide acylate ester was in accord with the hydrophil-lipophil balance (HLB) theory, similarly to other saccharide acylate esters. It is now expected that this compound will be useful as novel vaccine adjuvant which may induce both Th1 and Th2 type immune responses with low or no toxicity, not only as an vaccine emulsifier but in an aqueous suspension form.

Improvement of the systemic prime/oral boost strategy for systemic and local responses

This paper describes oral boost immunisations of primed animals as an alternative oral vaccination strategy. Mice were primed orally (PO), intranasally (IN), subcutaneously (SC), or intraperitoneally (IP) with ovalbumin (OVA) with or without adjuvant. Boost immunisations were given orally with or without cholera toxin (CT) as adjuvant. Prime immunisations induced variable IgA and IgG(1) titres in serum depending on the route. A subsequent oral boost increased these titres. Use of an adjuvant in the priming significantly increased serum IgA and, to a lesser extend, IgG(1). Oral boost immunisation induced significantly higher serum IgA titres in animals primed via the SC, IP and the IN route compared to the PO route. This was independent of the use of CT. Three oral boosts with OVA plus 5 microg CT given in 5 days to primed mice revealed higher IgA titres compared to single oral boosts and anti-OVA IgA titres in faeces were also detected. Finally, we put together our findings and propose a systemic priming/oral boost strategy in which mice were primed via the SC route with 100 microg OVA plus 50 microg Butyl16-p(AA), and subsequently orally boosted with three doses of 300 microg OVA plus 5 microg CT each. We concluded that oral immunisation is more effective in IN, SC, or IP primed mice than in PO primed mice, and that the IgA antibody response in serum and faeces can be improved by increasing the immunisation frequency and the use of appropriate adjuvants in primary and boost immunisation. The here-formulated strategy improves the probability of success of oral vaccination. The results are discussed in the light of the development of edible vaccines.

Protective antiviral immune responses to pseudorabies virus induced by DNA vaccination using dimethyldioctadecylammonium bromide as an adjuvant

To enhance the efficacy of a DNA vaccine against pseudorabies virus (PRV), we evaluated the adjuvant properties of plasmids coding for gamma interferon or interleukin-12, of CpG immunostimulatory motifs, and of the conventional adjuvants dimethyldioctadecylammonium bromide in water (DDA) and sulfolipo-cyclodextrin in squalene in water. We demonstrate that a DNA vaccine combined with DDA, but not with the other adjuvants, induced significantly stronger immune responses than plasmid vaccination alone. Moreover, pigs vaccinated in the presence of DDA were protected against clinical disease and shed significantly less PRV after challenge infection. This is the first study to demonstrate that DDA, a conventional adjuvant, enhances DNA vaccine-induced antiviral immunity.

Adjuvant effects of sulfolipo-cyclodextrin in a squalane-in-water and water-in-mineral oil emulsions for BHV-1 vaccines in cattle

The antibody and cell mediated immune responses induced by BHV-1 were analysed in cattle after vaccination and challenge exposure to the virulent strain LA of BHV-1. Animals were vaccinated intramuscularly (IM) with inactivated virus vaccines against BHV-1 containing either a water in mineral oil adjuvant (W/O), a water in mineral oil adjuvant plus Avridine (W/O+Avridine) or sulfolipo-cyclodextrin in squalane in-water emulsion (SL-CD/S/W). No significant differences were registered in the antibody response induced by the three evaluated vaccines. However, the BHV-1 specific cell-mediated immunite response was stronger and appeared earlier when SL-CD/S/W was included in the formulation. The efficacy of the vaccines was also evaluated after intranasal challenge of the calves with a virulent BHV-1 LA strain. Animals vaccinated with SL-CD/S/W had reduced virus excretion and clinical symptoms compared with the mock-vaccinated animals. Comparison of levels of BHV-1 specific IgG2 and IgG1 with virus shedding revealed that, regardless of the adjuvant administered, animals showing BHV-1 specific IgG2/IgG1 ratios higher than 1 were those with a significant lower number of individuals shedding virus. Additionally, animals vaccinated with SL-CD/S/W presented no post-vaccinal reactions. These factors, combined with the higher efficacy and the ease of manipulation of the biodegradable oil, makes the vaccine formulated with this new adjuvant an important contribution for the veterinary vaccines industry.

Alkyl-polyacrylate esters are strong mucosal adjuvants

Synthetic polymers were examined for their potency to enhance mucosal immune responses to inactivated antigens. Aqueous solutions of polyacrylic acid with a MW of 450 kDa (p[AA]) or an butyl-ester thereof with 16% esterification (Butyl16-p[AA]) plus antigen were administered twice intranasally in mice with a 2 week interval. The frequency of IgA-antibody secreting cells (ASCs) in lung cell suspensions was determined 1 week after the second immunisation. Both polymers significantly enhanced the IgA response against inactivated Newcastle disease virus (iNDV), inactivated influenza virus strain MRC-11 (iMRC-11), haemagglutinin/neuraminidase subunits of influenza virus strain A/Texas (HA/NA) and bovine serum albumin (BSA). Butyl16-p(AA) was significantly more effective than non-derivatised p(AA), cholera toxin B subunit (CTB) or liposomes. The factor of increase in IgA-ASCs varied from <10- to >100-fold and depended on the type of antigen, the dose of antigen and the adjuvant. Extremely high responses of about 10,000 IgA-ASCs per million lung cells were detected after immunisation with 5 microg HA/NA plus 50 microg Butyl16-p(AA). Intranasal immunisation with Butyl16-p(AA) resulted in high IgA responses, not only in the lungs, but also in the spleen and in high IgG responses in these organs. We concluded that alkyl-esters of polyacrylate are an interesting, novel category of mucosal adjuvants.

Effect of various adjuvants on secondary immune response in chickens

Stimulatory effects of several types of adjuvants on secondary antibody response to inactivated Newcastle disease virus (iNDV) were examined in chickens. For this purpose, animals were primed with iNDV without adjuvant resulting in a low but significant antibody response, boosted with iNDV plus adjuvant 3 weeks later, and analysed for specific antibody titres in serum 3 weeks after the booster. Water-in-mineral oil emulsion (W/O) caused significant increase in antibody titres measured in an indirect enzyme-linked immunosorbent (ELISA), haemagglutination inhibition (HI), and virus neutralisation (VN) assay. The adjuvants tested included three oil-in-water emulsions (i.e. mineral oil-in-water, sulpholipo(SL)-Ficoll400/squalane-in-water and sulpholipo-cyclodextrin/squalane-in-water), three negatively-charged polymers with high molecular weight (i.e. polyacrylate, polystyrenesulphonate and sulpho(S)-Ficoll400) and two surface-active agents (i.e. dimethyldioctadecylammonium bromide (DDA) and Quil A). These adjuvants enhanced significantly the secondary immune response but none reached the titre obtained with W/O. Combinations of adjuvants with distinct physicochemical properties, i.e. polyacrylate and DDA revealed only slight, beneficial effects. We concluded that the various types of adjuvants tested can stimulate secondary immune responses in primed animals but that W/O is superior.