Thermal Treatment of a Novel Saponin-Cholesterol Nanoparticle Vaccine Adjuvant Named NanoQuil F70 Secures a Uniform Morphology and Size Distribution

Abstract

Quil-A and cholesterol can, under certain conditions, form nanoparticles, but the conditions for the formation of a homogeneous population of a particular kind of particles with the same morphology and size have remained elusive. However, a well-defined uniformity, as well as a high degree of batch-to-batch consistency, are prerequisites for adjuvant formulations to be used for practical vaccines. To accomplish the above stated tasks in the present study, we demonstrated that Quil-A and cholesterol form well-defined worm-like stable particles with a mean diameter of around 40 nm by dynamic light scattering (DLS) under carefully controlled thermodynamical conditions with little or no Quil-A degradation. The nanoparticles thus prepared possessed a significantly reduced hemolytic effect in comparison to unformulated free Quil-A. However, when the same conditions were applied to QS-21/cholesterol nanoparticle formation the morphology achieved was coil spring-like particles with a mean diameter of around 70 nm. This discrepancy in particle morphology and size was attributed to the differences in hydrophobicity of the Quil-A, being a heterogenic fraction of acylated as well as deacylated saponins, and the QS-21. With the process optimizations leading to a standardized particle size distribution and nanoparticle morphology presented here, NanoQuil F70 holds the potential as a well-tolerated vaccine adjuvant for veterinary use raising a Th1/Th2 balanced immune response.