A novel method for preparing immune stimulating complexes (ISCOMs) by hydration of freeze-dried lipid matrix

The purpose of this study was to investigate the application of hydration of freeze-dried lipid monophase matrices as a novel technique to produce immune stimulating complexes (ISCOMs) encapsulating lipopeptides as potential sub-unit antigens. Size, polydispersity and morphology of the resulting colloidal particles were measured and characterized by photon correlation spectroscopy and transmission electron microscopy. The homogeneity of ISCOM preparations produced by this method was found to be influenced by the amount of matrix-forming material as well as the ratio of phospholipid:Quil A:cholesterol used for ISCOM preparation. Further, it was observed that more homogeneous ISCOM dispersions were produced if Quil A was included in the hydrating solution compared to incorporating Quil A in the lipid matrix. Entrapment of lipopeptide within ISCOMs was not affected by chain length (C12-C16) or the number of alkyl chains (1-3) and was greater than 80% when loaded at 5% w/w of total lipid. Entrapment efficiency was noted to decrease dramatically on increasing amount of lipopeptide in the ISCOMs from 5% to 10% of total lipid, decreasing to around 40%. All lipopeptide-loaded ISCOMs were observed to aggregate upon storage.