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ABSTRACT: Biocompatible lipid implants which promote the sustained release of antigen have potential as novel vaccine delivery systems for subunit antigen as they may reduce or remove the requirement for multiple administrations. Of particular interest are sustained release systems that release antigen incorporated into particles. Previous work has demonstrated that lipid implants prepared from phosphatidylcholine, cholesterol, the adjuvant Quil-A, and ovalbumin as the model antigen could stimulate an immune response equivalent to that induced by a prime and boost with a comparable injectable vaccine. However, entrapment of antigen into particles released from the implant was low. Therefore the aim of this study was to firstly determine if the inclusion of a cationic derivative of cholesterol, DC-cholesterol, into the implants increased antigen entrapment and immunogenicity, and secondly, if a cationic implant could induce at least a comparable immune response as compared to a prime and boost with an injectable vaccine. The inclusion of DC-cholesterol had only a minor effect on antigen entrapment into particles released from the implants and the implants did not stimulate cellular responses as effectively as the comparable injectable vaccine or the unmodified implant containing Quil-A and cholesterol, although the vaccine did induce stronger responses than either soluble protein alone, or protein co-delivered in alum.
International Journal of Pharmaceutics 08/2008; 363(1-2):91-8. · 3.35 Impact Factor
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ABSTRACT: A particulate vaccine delivery system consisting of cationic ISCOM derivatives (PLUSCOMs) was compared to classic anionic ISCOMs with regard to antigen attachment and ability to elicit in vivo T cell responses against a model protein antigen (ovalbumin [OVA]). ISCOMs did not incorporate hydrophilic OVA whilst OVA readily adsorbed onto PLUSCOMs with increasing adsorption at higher protein concentrations. The zeta-potential of PLUSCOMs significantly decreased with increasing protein load, suggesting neutralization of the cationic charge upon absorption of the anionic OVA. Antigen-specific CD8 T cell responses were demonstrated in mice vaccinated with either PLUSCOMs or ISCOMs. Ex vivo restimulation of harvested T cells demonstrated that cells isolated from PLUSCOM and ISCOM vaccinated mice responded to the secondary OVA challenge more efficiently than mice vaccinated with OVA in solution. Restimulated cells from the mice vaccinated with particulate vaccines produced significantly more INF-gamma. Therefore PLUSCOMs are as effective as classic ISCOMs in inducing antigen-specific CD8 T cell responses and have advantages with regard to the incorporation of purified anionic antigens.
Vaccine 07/2008; 26(35):4549-56. · 3.77 Impact Factor
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ABSTRACT: Sustained-release vaccines offer the potential to reduce, or obviate, the need for repeated dosing of vaccines. In this study, we report the development and characterisation of sustained-release lipid implants that release immunogenic, self-assembling colloidal particles. Lipid implants consisting of cholesterol (CHOL), phosphatidylcholine (PC), the adjuvant Quil-A (QA) and the model antigen ovalbumin (OVA) were formulated and investigated using a variety of techniques. Transmission electron microscopy was utilised to demonstrate the release of colloidal structures from these implants over time. The nature of the colloidal particles varied depending on the ratio of QA:CHOL:PC. The release of the model antigen as well as its incorporation into the colloidal particles was investigated using a fluorescent tag covalently coupled to OVA and quantified using fluorospectrophotometry. The antigen release was modified by the incorporation of excess CHOL into the formulation and was not only dependent on the ratio of QA:CHOL:PC but also on the nature of the model antigen. Alteration of the hydrophobicity of the model antigen resulted in an increased incorporation into the colloidal structures. Surface changes of the implants were analysed using scanning electron microscopy. The implant formulations investigated in this study show a potential for the delivery of subunit vaccines.
Journal of Drug Targeting 05/2008; 16(3):213-23. · 2.70 Impact Factor
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ABSTRACT: Sustained-release formulations have drawn the attention of formulation scientists working in the area of vaccine research because these systems may reduce the need for booster immunisations. This would be of great advantage especially for the administration of subunit vaccines. The aim of this study was to illustrate the performance of liposome-forming, sustained-release lipid implants containing 2% of the adjuvant Quil-A (QA) (w/w of total lipids) and ovalbumin (OVA) as a model antigen, in an in vivo study using C57Bl/6 mice. QA/OVA-containing lipid implants were administered subcutaneously and stimulated a similar magnitude of immune response when compared with an immediate-release formulation that contained an equivalent amount of adjuvant and antigen but was administered twice. The novel implant system presented here combines the advantages of both sustained release and particulate delivery in one formulation.
Journal of Drug Targeting 05/2008; 16(3):224-32. · 2.70 Impact Factor
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ABSTRACT: ISCOM matrices constitute colloidal structures formed from Quillaja saponins, cholesterol and phospholipid. Addition of protein antigens to these matrices leads to the formation of ISCOMs. In this review we report on microscopic investigations of ISCOM matrices and ISCOMs as well as related colloidal structures, such as helices, worm-like micelles, ring-like micelles, and lamellae structures. We briefly outline the immunologic basis for the use of ISCOMs as vaccine delivery systems, and describe the various methods to form ISCOMs. Negative staining transmission electron micrographs of all colloidal structures are presented and described. On the basis of our microscopic investigations, different formation mechanisms of ISCOMS are discussed.
Micron 02/2006; 37(8):724-34. · 1.53 Impact Factor
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ABSTRACT: This study describes the formation of cationic, cage-like complexes which have a structure similar to classic anionic ISCOMs. In order to prepare these complexes cholesterol, a major component of classic ISCOM formulations, was substituted with a cationic derivative, 3beta-[N-(N',N'-dimethylaminoethane)-carbamoyl]-cholesterol (DC-CHOL). Colloidal dispersions with varying compositions of DC-CHOL, phosphatidylcholine, and Quil-A, which is a mixture of anionic triterpene saponins, were prepared by the lipid-film hydration method and characterised by transmission electron microscopy and laser Doppler electrophoresis. The colloidal structures obtained are presented in pseudo-ternary phase diagrams with two buffer systems as the pseudo-component. It was found that the formation of cationic, cage-like particles is highly depending on the formulation buffer. With TRIS buffered saline (TBS) pH 7.4, cage-like particles formed at compositions with high proportions of DC-CHOL and had a strongly positive zeta-potential. These could be purified by differential centrifugation. With phosphate buffered saline pH 7.4, the formation of cage-like particles was much reduced. It was shown that the formation of cage-like particles with a positive charge depended on suitable concentrations of TRIS in the hydration buffer.
Journal of Pharmaceutical Sciences 09/2005; 94(8):1794-807. · 3.06 Impact Factor
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ABSTRACT: This study describes the formulation of immuno-stimulating complexes (ISCOMs) utilising the ethanol injection technique. Cholesterol and phosphatidylcholine were dissolved in ethanol and the resulting solution was rapidly injected into a stirred, aqueous solution of the triterpene-saponin mixture Quil-A. The reversed experiment was also carried out by adding the aqueous Quil-A solution to a solution of cholesterol/phosphatidylcholine dissolved in ethanol. This was done by either rapid injection or dropwise addition of the aqueous Quil-A solution. The colloidal dispersions obtained by ethanol injection and reversed addition were compared with formulations obtained by the dialysis and lipid-film hydration methods. In a further experiment, the preparation of ISCOMs from liposomes as precursor structures was investigated. Transmission electron microscopy was used to analyse the resulting colloidal dispersions. Samples were also compared with respect to homogeneity of obtained particle species. The ethanol injection technique led to formation of ISCOMs in high numbers within 2 h post formulation. The reversed rapid injection resulted in a similar colloidal dispersion, differing from the former mainly due to the presence of some helical micellar structures. The reversed, dropwise addition led to the formation of helices as the predominant colloidal structure. Of the three previously established methods, only dialysis led to the formation of ISCOMs within 48 h. The lipid-film hydration method and the approach using liposomes as precursor structures did not produce ISCOMs under the conditions and within the time periods investigated. However, it is known that dispersions prepared by the hydration method equilibrate towards ISCOMs after longer storage. Ethanol injection and reversed rapid injection are simple, cost-effective and quick methods to produce ISCOMs.
Journal of Pharmacy and Pharmacology 07/2005; 57(6):729-33. · 2.17 Impact Factor
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ABSTRACT: Advances in vaccine formulation have seen a trend towards the use of subunit antigens, ideally incorporated into particulate carriers. These systems are usually in the nanometer size range to facilitate uptake into antigen-presenting cells and to mimic the nature of pathogens. In addition, adjuvants can be incorporated into the same carrier and therefore result in the simultaneous delivery of antigen and adjuvant to the same antigen-presenting cell. A wide variety of particu-late carriers have been investigated for vaccine delivery ranging from biological-based particles such as bacterial ghosts and virus-like particles to more simple polymer-or lipid-based systems. In this review we will focus on lipid-based par-ticulate carriers as these offer great potential as regards immune stimulation and due to the simple formulation techniques involved are likely to be more easily scaled-up for manufacture. Another advantage of such systems is versatility in that in addition to the subcutaneous administration of these vaccine formulations, there is also potential for transdermal or even oral delivery. Examples of such delivery systems include liposomes, ethosomes, transfersomes, bilosomes, and immune stimulating complexes. The physico-chemical properties of such systems will be reviewed as will their potential to stimu-late immune responses. In addition, we will summarise the recent developments in lipid-based sustained delivery systems for antigens.
