Colloidal characteristics and formulation of pure protein particulate vaccines

We recently reported that dense gas processing of the protein ovalbumin (OVA) resulted in the formation of particles that were insoluble in water and which retained their immunogenicity in vivo. In the present study, the colloidal properties of these pure protein particles were investigated to in part inform rational formulation approaches.

The colloidal properties of the particles, in terms of size, zeta potential and pH-dependent surface and solution properties, were examined.

In phosphate-buffered saline (pH7.4), flocculation of the particles was observed, which was prevented when particles were suspended in acetate buffer at pH lower than 4. The resulting particle size was 300nm with low polydispersity and zeta potential of 22.9±3.1mV (mean±SEM, n=3) at pH3. Dense gas OVA particles were also prevented from flocculation using steric stabilisation with Pluronic F127. In this form the particles were stable in Krebs-Henseleit solution for 48h at room temperature.

These findings indicate that insoluble pure protein particles produced by dense gas processing have desirable characteristics as particulate vaccines, including consistency of particle size under controlled conditions and high colloid stability.