Sorbitan monostearate polysolbate 20 organogels containing niosomes: a delivery vehicle for antigens?

Multi-component organogels formed using the non-ionic surfactant sorbitan m onostearate as gelator have been formulated to contain niosomes. The purpos e of this study was to evaluate the potential of these vesicle-in-water-in- oil (v/w/o) gels as delivery vehicles for vaccines. Bovine serum albumin (B SA) and haemagglutinin (HA) were used as model antigens in depot and immuno genicity studies respectively. The complex gels were prepared by the additi on of a hot (60 degrees C) aqueous niosome suspension (v/w) to the sol phas e (o, an organic solution of the gelator); a vesicle-in-water-in-oil (v/w/o ) emulsion was produced which cools to an opaque, semi-solid, thermoreversi ble v/w/o gel. Light microscopy of the organogel revealed that the microstr ucture consists of a tubular network of surfactant aggregates in the organi c medium, the niosome suspension being dispersed in these surfactant tubule s. Therefore, in such gels, the vaccine is thought to be entrapped in the n iosomes, themselves located within the sorbitan monostearate tubular networ k in the organic medium. In vivo, a depot effect was observed following int ramuscular administration of the gel containing the entrapped bovine serum albumin, cleared from the injection site over a period of days. The relativ ely short-lived nature of the depot was thought to arise due to interaction s between the gel and the local interstitial fluid which results in gel dis integration in situ. Thus, the niosomes containing antigens are believed to be released from the organic gel. Immunogenicity studies showed that the v /w/o gel as well as one of the controls, the water-in-oil (w/o) gel, posses s immunoadjuvant properties and enhance the primary and secondary antibody titres (of total IgG, IgG(1), IgG(2a) and IgG(2b)) to haemagglutinin antige n. As far as humoral immunity is concerned, the w/o gel showed stronger imm unoadjuvant properties compared to the v/w/o gel, being effective at a lowe r antigen dose i.e 0.1 mu g HA. (C) 1999 Elsevier Science B.V. All rights r eserved.