Lipid-based Systems Research Articles

Targeted lipid-based systems for siRNA delivery

Gene silencing agents, like small interfering RNA (siRNA), are powerful tools widely used in therapeutic and fundamental studies. However, major limitations to their in vivo and in vitro application have been recognized. Therefore, efficient delivery vehicles are essential for siRNA application in therapeutics. Lipid-based systems, such as liposomes, have been extensively and successfully used as nucleic acid vectors. In this review the major obstacles to siRNA delivery are discussed, as well as the most recent advances regarding the development of nanocarriers designed for such a purpose. Cationic liposomes and targeted stabilized nucleic acid liposomes are described in detail, as they are considered promising tools to mediate intracellular delivery of gene silencing agents. Additionally, the advantages of cellular targeting and long circulation times are discussed. Moreover, combination of drugs and siRNA in the same delivery system is presented as a promising strategy, allowing different molecular targets to be reached within a specific cell population, with a single therapeutic system.

SiRNA Delivery with Lipid-based Systems: Promises and Pitfalls

A key hurdle for the further development of RNA interference (RNAi) therapeutics like small interfering RNA (siRNA) is their safe and effective delivery. Lipids are promising and versatile carriers because they are based on Nature's own building blocks and can be provided with properties which allow for protection of the siRNA, steric stabilization, targeting, membrane fusion and triggered drug release. At present a variety of lipid-based transfectants for siRNA delivery have been used for in vitro and in vivo purposes. The majority bears a cationic charge to electrostatically complex the siRNA into more hydrophobic lipoplexes, which promote passage of the siRNA across cellular membrane barriers, especially when lipids are added that facilitate membrane fusion. Despite these attractive features, siRNA delivery vehicles are facing a number of challenges such as the limited delivery efficiency in vivo, toxicity and non-specific stimulation of the immune system. To optimally design and tailor the lipidic systems for siRNA delivery, better insight is needed into the mechanisms of cell delivery. More specifically, further clarification is need regarding the nature of cell surface interactions, routes of internalization, passage of intracellular membranes, and mechanisms of immune activation. This review provides an overview of the main constituents currently employed in lipid-based siRNA carriers, and recent research into improvements of cell delivery. In addition, pitfalls related to immune activation and side effects are discussed, and possible ways to overcome them are highlighted.

Preparation of Multicompartment Lipid-Based Systems Based on Vesicle Interactions

Various strategies for constructing artificial multicompartment vesicular systems, which primitively mimic the structure of eukaryotic cells, are presented. These model systems are appropriate for addressing several issues such as the understanding of cell processes, the development of nanoreactors and novel multicompartment delivery systems for specific drug applications, the transport through bilayer membranes, and also hypothesizing on the evolution of eukaryotic cells as originating from the symbiotic association of prokaryotes.

Formation of Kinetically Trapped Nanoscopic Unilamellar Vesicles from Metastable Nanodiscs

Zwitterionic long-chain lipids (e.g., dimyristoyl phosphatidylcholine, DMPC) spontaneously form onion-like, thermodynamically stable structures in aqueous solutions (commonly known as multilamellar vesicles, or MLVs). It has also been reported that the addition of zwitterionic short-chain (i.e., dihexanoyl phosphatidylcholine, DHPC) and charged long-chain (i.e., dimyristoyl phosphatidylglycerol, DMPG) lipids to zwitterionic long-chain lipid solutions results in the formation of unilamellar vesicles (ULVs). Here, we report a kinetic study on lipid mixtures composed of DMPC, DHPC, and DMPG. Two membrane charge densities (i.e., [DMPG]/[DMPC] = 0.01 and 0.001) and two solution salinities (i.e., [NaCl] = 0 and 0.2 M) are investigated. Upon dilution of the high-concentration samples at 50 °C, thermodynamically stable MLVs are formed, in the case of both weakly charged and high salinity solution mixtures, implying that the electrostatic interactions between bilayers are insufficient to cause MLVs to unbind. Importantly, in the case of these samples small angle neutron scattering (SANS) data show that, initially, nanodiscs (also known as bicelles) or bilayered ribbons form at low temperatures (i.e., 10 °C), but transform into uniform size, nanoscopic ULVs after incubation at 10 °C for 20 h, indicating that the nanodisc is a metastable structure. The instability of nanodiscs may be attributed to low membrane rigidity due to a reduced charge density and high salinity. Moreover, the uniform-sized ULVs persist even after being heated to 50 °C, where thermodynamically stable MLVs are observed. This result clearly demonstrates that these ULVs are kinetically trapped, and that the mechanical properties (e.g., bending rigidity) of 10 °C nanodiscs favor the formation of nanoscopic ULVs over that of MLVs. From a practical point of view, this method of forming uniform-sized ULVs may lend itself to their mass production, thus making them economically feasible for medical applications that depend on monodisperse lipid-based systems for therapeutic and diagnostic purposes.

Imaging of blood plasma coagulation at supported lipid membranes

The blood coagulation system relies on lipid membrane constituents to act as regulators of the coagulation process upon vascular trauma, and in particular the 2D configuration of the lipid membranes is known to efficiently catalyze enzymatic activity of blood coagulation factors. This work demonstrates a new application of a recently developed methodology to study blood coagulation at lipid membrane interfaces with the use of imaging technology. Lipid membranes with varied net charges were formed on silica supports by systematically using different combinations of lipids where neutral phosphocholine (PC) lipids were mixed with phospholipids having either positively charged ethylphosphocholine (EPC), or negatively charged phosphatidylserine (PS) headgroups. Coagulation imaging demonstrated that negatively charged SiO2 and membrane surfaces exposing PS (obtained from liposomes containing 30% of PS) had coagulation times which were significantly shorter than those for plain PC membranes and EPC exposing membrane surfaces (obtained from liposomes containing 30% of EPC). Coagulation times decreased non-linearly with increasing negative surface charge for lipid membranes. A threshold value for shorter coagulation times was observed below a PS content of ∼6%. We conclude that the lipid membranes on solid support studied with the imaging setup as presented in this study offers a flexible and non-expensive solution for coagulation studies at biological membranes. It will be interesting to extend the present study towards examining coagulation on more complex lipid-based model systems.

The effect of neutral helper lipids on the structure of cationic lipid monolayers

Successful drug delivery via lipid-based systems has often been aided by the incorporation of 'helper lipids'. While these neutral lipids enhance the effectiveness of cationic lipid-based delivery formulations, many questions remain about the nature of their beneficial effects. The structure of monolayers of the cationic lipid dimethyldioctadecylammonium bromide (DODAB) alone, and mixed with a neutral helper lipid, either diolelyphosphatidylethanolamine or cholesterol at a 1 : 1 molar ratio was investigated at the air-water interface using a combination of surface pressure-area isotherms, Brewster angle microscopy (BAM) and specular neutron reflectivity in combination with contrast variation. BAM studies showed that while pure DODAB and DODAB with cholesterol monolayers showed fairly homogeneous surfaces, except in the regions of phase transition, monolayers of DODAB with diolelyphosphatidylethanolamine were, in contrast, inhomogeneous exhibiting irregular bean-shaped domains throughout. Neutron reflectivity data showed that while the thickness of the DODAB monolayer increased from 17 to 24 Å as it was compressed from a surface pressure of 5-40 mN m(-1), the thickness of the helper lipid-containing monolayers, over the same range of surface pressures, was relatively invariant at between 25 and 27 Å. In addition, the monolayers containing diolelyphosphatidylethanolamine were found to be more heavily hydrated than the monolayers of cationic lipid, alone or in combination with cholesterol, with hydration levels of 18 molecules of water per molecule of lipid being recorded for the diolelyphosphatidylethanolamine-containing monolayers at a surface pressure of 30 mN m(-1) compared with only six and eight molecules of water per molecule of lipid for the pure DODAB monolayer and the cholesterol-containing DODAB monolayer, respectively.

Lovastatin Nanoparticle Synthesis and Characterization for Better Drug Delivery

Nano drug delivery system is the latest technology employed in various medicinal applications. This technol- ogy can be adapted to the conventional drug administration due to its site-specific targeting phenomena. The oral lipo- philic drug administration has its drawbacks due to poor solubility and bioavailability. Lipid-based carrier systems are now widely popular due to improved efficiency, especially for lovastatin delivery. Lovastatin is an important drug which arrests the rate-limiting step of the cholesterol cascade. This drug has short half-lives, poor oral-administered bioavailabil- ity, poor solubility, and is rapidly metabolizable. Based on the composition, the drug delivery carriers are classified into solid lipid nanoparticles (SLNs), lipid emulsions (LEs), and nanostructured lipid carriers (NLCs). Among them, NLCs are a smarter generation of drug delivery carriers for lovastatin. The selection of various lipid systems and their formulation are discussed in this paper. Moreover, the characterization of these carrier systems to achieve the optimal characteristic features is discussed in a concise manner.

Lipid-based colloidal systems (nanoparticles, microemulsions) for drug delivery to the skin: materials and end-product formulations

Drug delivery to or via the skin presents both unique opportunities and obstacles due to skin structure, physiology, and barrier properties. The skin, the largest organ of the body, may be viewed either as a natural protective barrier against penetration of toxic exogenous compounds, excessive loss of water and other essential compounds, or as a promising portal of entry for drugs for local and/or systemic action. Many novel lipid nanocarriers have been designed for topical application of drugs since they allow these molecules to overcome the skin barrier and improve cutaneous bioavailability. The increased drug absorption is often a consequence of a reversibly disrupted barrier function of the skin by the vehicle itself or by specific ingredients figuring in the topical formulation that act as penetration enhancer. Micro/nanoemulsions and lipid nanoparticles are known to provide several advantages over conventional formulations in terms of stability and skin penetration enhancement. However, their characteristics in the original form are low viscous liquids and colloidal dispersions. Therefore, their topical application may be limited in some cases. This review describes recent works in formulating lipid nanocarriers, especially in the semi-solids and hydrogels forms, and reports their special features for biomedical and dermocosmetic applications.

Recent developments in lipid-based pharmaceutical nanocarriers

Within the broad spectrum of nanoparticulate carriers, polymeric and lipid-core micelles, liposomes, solid nanoparticles and many others have demonstrated great biological properties which make them excellent pharmaceutical delivery systems. In particular, micelles and liposomes have been shown to have good longevity in the blood that allows their accumulation in pathological areas with a compromised vasculature; can possess specific targeting to disease sites when various targeting ligands are attached to the surface of the nanocarriers or to surface-attached cell-penetrating molecules (like TAT peptide) to enhance intracellular penetration; possess stimulus-sensitivity allowing for drug release from the carriers under certain pathological conditions; and show contrast properties with carrier loading of various contrast materials that allow for direct carrier visualization in vivo. The engineering of "multifunctional pharmaceutical nanocarriers" based on the combination of several useful properties in the same system can significantly enhance the efficacy of many therapeutic and diagnostic protocols. This review considers the current status and next future directions in the emerging area of nanomedicine with particular attention to two lipid-based nanoparticulate systems: liposomes and micelles.

Oral fondaparinux: use of lipid nanocapsules as nanocarriers and in vivo pharmacokinetic study

Oral anticoagulant therapy could be advanced using lipid-based nanoparticulate systems. This study examined lipid nanocapsules for their oral absorption potential as the first step in developing oral fondaparinux (Fp) novel carriers. Using phase inversion method and cationic surfactants such as hexadecyltrimethyl ammonium bromide (CTAB) or stearylamine (SA), cationic lipid nanocapsules (cLNCs), loaded with Fp on their surface, were prepared and characterized (zeta potential, size and Fp association efficiency and content). In vivo studies were conducted after single oral increasing doses of Fp-loaded cLNCs (0.5 to 5 mg/kg of Fp) in rats and the concentration of Fp in the plasma was measured by anti-factor Xa activity assay. The monodisperse, (~50 nm), positively charged Fp-cLNCs with high drug loadings demonstrated linear pharmacokinetic profiles of the drug with an increased oral absolute bioavailability (up to ~21%) compatible with therapeutic anticoagulant effect (>0.2 μg/mL).

Properties, Engineering and Applications of Lipid-Based Nanoparticle Drug-Delivery Systems: Current Research and Advances

Lipid-based drug-delivery systems have evolved from micro- to nano-scale, enhancing the efficacy and therapeutic applications of these delivery systems. Production of lipid-based pharmaceutical nanoparticles is categorized into top-down (fragmentation of particulate material to reduce its average total dimensions) and bottom-up (amalgamation of molecules through chemical interactions creating particles of greater size) production methods. Selection of the appropriate method depends on the physiochemical properties of individual entities within the nanoparticles. The production method also influences the type of nanoparticle formulations being produced. Liposomal formulations and solid-core micelles are the most widely utilized lipid-based nanoparticles, with surface modifications improving their therapeutic outcomes through the production of long-circulating, tissue-targeted and/or pH-sensitive nanoparticles. More recently, solid lipid nanoparticles have been engineered to reduce toxicity toward mammalian cells, while multifunctional lipid-based nanoparticles (i.e., hybrid lipid nanoparticles) have been formulated to simultaneously perform therapeutic and diagnostic functions. This article will discuss novel lipid-based drug-delivery systems, outlining the properties and applications of lipid-based nanoparticles alongside their methods of production. In addition, a comparison between generations of the lipid-based nano-formulations is examined, providing insight into the current directions of lipid-based nanoparticle drug-delivery systems.

Bicontinuous cubic liquid crystals as sustained delivery systems for peptides and proteins

Importance of the field: Self-assembling lipid-based liquid crystalline systems are a broad and active area of research. Of these mesophases, the cubic phase with its highly twisted bilayer and two non-intersecting water channels has been investigated extensively for drug delivery. The cubic phase has been shown to accommodate and control the release of drugs with varying physicochemical properties. Also, the lipids used to prepare these delivery systems are generally cheap, safe and biodegradable, making these systems highly attractive. Early research investigating the potential of cubic phases as delivery systems showed that several peptides or proteins entrapped within these gel-based systems showed retarded release. Furthermore, entrapment within the cubic phase protected the selected peptide or protein from chemical and physical degradation with its native confirmation and bioactivity retained.Areas covered in this review: In this review, the literature pertaining to the delivery of various bioactives from cubic liquid crystalline phases is examined, with a particular focus on peptides and proteins. The scope and limitations of the cubic phases in this respect and the future of cubic liquid crystalline systems as sustained delivery systems are highlighted.What the reader will gain: The reader will be able to gain an understanding of the properties of the bicontinuous cubic phase and how its structural attributes make these systems desirable for sustained delivery of bioactives, in particular peptides and proteins, but also how these same structural properties have hindered progress towards clinical applications. Current strategies to overcome these issues will also be discussed.Take home message: The bicontinuous cubic phase offers great potential in the field of peptide and protein delivery, but limited research in this area precludes definite conclusions to its future in this respect.

Lipid‐based nanotherapeutics for siRNA delivery

RNA interference (RNAi) is a specific gene-silencing mechanism triggered by small interfering RNA (siRNA). The application of RNAi in the clinic requires the development of safe and effective delivery systems. Inspired by progress with lipid-based systems in drug delivery, efforts have been dedicated to the development of liposomal siRNA delivery systems. Many of the lipid-based delivery vehicles self-assemble with siRNA through electrostatic interactions with charged amines, generating multi-lamellar lipoplexes with positively charged lipid bilayers separated from one another by sheets of negatively charged siRNA strands. Internalization of lipid-based siRNA delivery systems into cells typically occurs through endocytosis; accordingly, delivery requires materials that can facilitate endosomal escape. The size of the carrier is important as carriers <100 nm in diameter have been reported to have higher accumulation levels in tumours, hepatocytes and inflamed tissue, whereas larger particles tend to be taken up by Kupffer cells or other components of the reticuloendothelial system (RES). To reduce RES uptake and increase circulation time, carriers have been modified on the surface with hydrophilic materials, such as polyethyleneglycol. Herein, we review the molecular and structural parameters of lipid-based siRNA delivery systems.

Lipid-Based Nanoparticulate Systems for the Delivery of Anti-Cancer Drug Cocktails: Implications on Pharmacokinetics and Drug Toxicities

The use of drug cocktails has become a widely adopted strategy in clinical cancer therapy. Cytotoxic drug cocktails are often administered based on maximum tolerated dose (MTD) of each agent, with the belief of achieving maximum cell kill through tolerable toxicity level. Yet, MTD administration may not have fully captured the therapeutic synergism that exists among the individual agents in the drug cocktail, as the response to a cocktail regimen, that is, whether the effect is synergistic or not, could be highly sensitive to the concentration ratios of the individual drugs at the site of action. It is important to realize that the inherently different pharmacokinetic profiles of the individual agents could have significant influence on the response to an anti-cancer drug cocktail by dictating the amount of the individual agents reaching the tumor site and therefore the concentration ratios. Furthermore, the individual agents may have unfavorable pharmacokinetic interactions that add to the difficulty in determining the therapeutic and/or toxicological effects of the drug cocktail. In this review, we will focus on how lipid-based nanoparticulate systems could address the above issues associated with anti-cancer drug cocktails. Specifically, we will highlight the use of liposome systems as the means to control and coordinate the delivery of various anti-cancer drug cocktails, encompassing conventional chemotherapeutics, chemosensitizing agents and molecularly targeted agents.

Self-Assembled Lipid Nanomedicines for siRNA Tumor Targeting

Lipid-based nanoparticle technology has developed from chemical drug carrier into an efficient multifunctional siRNA tumor targeting delivery system. In this review, we start with an overview of the lipid-based nanomedicine history and the two classes of lipidic vectors for DNA or siRNA delivery. Then we discuss the features of lipid-based nanomedicine that lead to effective tumor targeting and the principles behind. We also discuss nanoparticle surface modification, classes of tumor targeting ligands, and other state-of-the-art strategies for enhancing endosome release primarily focused on lipid-based systems. At the end, we show that multifunctional self-assembled lipid-based nanoparticles could also be versatile delivery vehicles for cancer molecular imaging probes.

Lipophilisation enzymatique de composés phénoliques et évaluation de leurs propriétés antioxydantes

L'oxydation des lipides insatures, qui constitue l'une des causes majeures de l'alteration des produits alimentaires et cosmetiques, peut etre limitee par l'emploi d'antioxydants. Les composes phenoliques, et plus particulierement les acides phenoliques et les flavonoides, suscitent un interet grandissant pour leurs proprietes antioxydantes. Cependant, la mise en oeuvre de ces molecules polaires dans les matrices lipidiques (de type emulsion ou autre) est delicate et peut s'accompagner d'une diminution de leur efficacite. Pour contourner ce probleme, l'une des strategies consiste a ajuster la polarite de ces molecules par le greffage de chaines aliphatiques de longueurs differentes. La premiere partie de ce travail a ete consacree a la synthese enzymatique d'une serie d'esters lipophiles des acides chlorogenique et rosmarinique. Concernant l'acide chlorogenique, les meilleurs resultats ont ete obtenus en utilisant une strategie en deux etapes. Cette strategie correspond a une esterification prealable au methanol en presence d'une resine sulfonique suivie d'une transesterification enzymatique (lipase B de Candida antarctica) du chlorogenate de methyle en milieu fondu, avec des alcools de longueurs de chaine comprise entre 4 et 16 atomes de carbone. En conditions optimales, les vitesses initiales de transesterification s'averent jusqu'a deux fois superieures aux vitesses d'esterification enzymatique directe. Par ailleurs, la strategie en deux etapes conduit a des rendements globaux de 61 a 93% contre 40 a 60% dans le cas de l'esterification directe. Concernant l'acide rosmarinique, seule l'esterification directe en presence de resine sulfonique a permis d'atteindre des rendements satisfaisants (de 82% a 99%, selon la longueur de la chaine greffee). Dans la deuxieme partie de ce travail, nous avons evalue, d'un point de vue cinetique et stationnaire, l'impact de la lipophilisation sur la capacite des nouvelles molecules a pieger le radical stable 2,2-diphenyl-1-picryihydrazyl (DPPH*). Les donnees cinetiques montrent que l'acide chlorogenique se stabilise sous sa forme quinone, tandis que les esters tendent a former des dimeres a partir de leurs formes semi-quinone. Les resultats obtenus a l'etat stationnaire indiquent que les acides chlorogenique et rosmarinique, mais egalement leurs esters . respectifs, ont une capacite reductrice superieure a la capacite theorique imputable aux nombre d'hydroxyles phenoliques. Ces resultats peuvent etre expliques en considerant l'existence de reactions de regeneration et/ou de dimerisation. Enfin, la troisieme partie de ce travail a ete consacree a l'evaluation de la capacite antioxydante des derives lipophilises d'acides chlorogenique et rosmarinique en milieu emulsionne, par une nouvelle methodologie appelee test des Menes conjugues autoxydables (CAT). Les resultats ont montre que l'augmentation de la longueur de chaine aliphatique ne conduisait pas forcement a une amelioration de la capacite antioxydante comme le predit le «Paradoxe Polaire». En effet, un maximum de la capacite antioxydante pour des longueurs de chaine de 12 et 8 atomes de carbone a ete observe pour les derives lipophiles des acides chlorogenique et rosmarinique respectivement. Les principales hypotheses avancees pour expliquer ce comportement inattendu sont basees sur la repartition des antioxydants et de leurs formes oxydees entre les diverses phases du systeme reactionnel. (Resume d'auteur)

Status and future prospects of lipid-based particulate delivery systems as vaccine adjuvants and their combination with immunostimulators

Vaccines seek to adopt pathogen-like characteristics but not true pathogen characteristics to activate the immune system without causing life-threatening disease. Vaccine formulations are therefore often particulate in nature, with dimensions comparable to pathogens, and often contain highly conserved pathogen-associated molecular patterns as adjuvants stimulating the immune system. Only a few adjuvants have been approved for human use. There is therefore an unmet medical need for the development of effective and safe adjuvants that can stimulate cellular, humoral or mucosal immunity, or combinations thereof, depending on the requirements, to prevent the specific disease. Lipid-based particulate systems are in this respect promising and versatile adjuvants that can be customized rationally towards specific vaccine targets by varying their composition. In this review, current progress in the development of lipid-based vaccine delivery systems is discussed, with a special focus on emulsions, liposomes and immune-stimulating complexes, and their combination with immunostimulatory compounds. Formulations, adjuvant mechanisms and alternative administration routes are highlighted.

Studies on tamoxifen encapsulated in lipid vesicles: Effect on the growth of human breast cancer MCF-7 cells

Tamoxifen is a nonsteroidal estrogen-receptor modulator widely used in the treatment of breast cancer. Apoptosis has been reported to be a major mechanism for its antitumor effect. In the current studies, an endeavor was made to investigate the efficacy of vesicularly encapsulated tamoxifen on human breast cancer MCF-7 cells. Phospholipid-based vesicular systems viz. conventional liposomes and elastic-membrane liposomes were employed to encapsulate the drug. The MTT colorimetric assay was used to determine the efficacy of the tested formulations. The results demonstrated composition-dependent strong inhibition in the viability of MCF-7 cells with encapsulated tamoxifen vis-à-vis free drug. The encouraging findings from the current work construe immense potential of the lipid-based vesicular systems in the treatment of breast cancer.

Lipid-based emulsion system as non-viral gene carriers

The genetic materials for systemic administration meet a number of hurdles before they reach the nucleus of the target cells, such as enzymatic degradation in the bloodstream, extravascularization around the target tissue, endocytosis by the target cells, and endosomal escape of the genes. Therefore, there have been tremendous needs of effective gene carriers that can deliver the genetic materials to the target site. Of numerous approaches, recent studies have demonstrated that the lipid-based emulsion systems have the high potential as non-viral gene carriers: 1 lipid emulsions are biocompatible because their major constituents are composed of the non-toxic oils and amphiphilic lipids; 2 the cationic lipid emulsions can form nano-sized complexes with negatively charged DNAs, through which the genetic materials can be protected from the enzymatic degradation in the body fluids; 3 The emulsion/DNA complexes are shown to be stable in the bloodstream since their surfaces are rarely recognized by the immune-related cells and serum proteins; and 4 the surfaces of the emulsion complexes are readily modified by varying the lipid composition. In this review, highlighted are the recent advances in the emulsion-based gene carriers.

Advances in Lipid-Based Subunit Vaccine Formulations

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 particulate 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 particulate 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 stimulate immune responses. In addition, we will summarise the recent developments in lipid-based sustained delivery systems for antigens. Keywords: Vaccine, immune response, lipids, particulate delivery, scale-up