On the dilution behaviour of immuno-stimulating complexes (ISCOMs)

Area of Science:

• Biochemistry
• Immunology
• Materials Science

Background:

• Immunostimulating complexes (ISCOMs) are effective vaccine delivery systems.
• Their characteristic cage-like structure is linked to potency, but mechanisms remain unclear.
• ISCOMs are composite mixed micelles containing Quillaja saponin surfactant.

Purpose of the Study:

• To investigate the micelle to vesicle transition of ISCOMs upon dilution.
• To understand how dilution affects ISCOM structure and composition.
• To explore the relevance of these changes for ISCOM applications.

Main Methods:

• Preparation of ISCOM matrices via dialysis.
• Analysis of structural changes using transmission electron microscopy (TEM).
• Characterization of particle size, polydispersity, and zeta-potential using dynamic light scattering (DLS).

Main Results:

• Dilution induced a step-wise morphological transition from cage-like structures to helical micelles and small lipidic particles.
• Dynamic light scattering revealed increased particle size and polydispersity with dilution.
• Zeta-potential changes indicated saponin release from the lipid matrix upon dilution.

Conclusions:

• ISCOMs undergo significant structural changes upon aqueous dilution, including saponin release.
• This dissociation of Quillaja saponins may be a key factor in ISCOM immunostimulatory activity.
• Understanding these dilution-induced transitions is crucial for optimizing ISCOM-based vaccines.