Use of Oil-Based Adjuvants in Vaccine Applications

The design of emulsions for adjuvant application involves several parameters. The nature and amount of emulsion components have a significant impact not only on the physical and chemical stability of the final products, but also on the immune response and adverse reactions after vaccination. The oil preference for the emulsion should also be considered. Several studies show that poorly metabolized mineral oil has superior efficacy in vaccine formulation compared to plant-derived oils. In addition, the appropriate surfactant concentration must be determined to produce a stable emulsion while avoiding excessive amounts. Adverse reactions have been reported after vaccination with surfactants at high concentrations in emulsions.

Insufficient knowledge of the relationship between the size of emulsion droplets and the quality and quantity of immune responses is an important limiting factor for the rational design of emulsion-based adjuvants. A recent study showed that emulsions with a droplet size of 160 nm produced significantly higher antibody responses in mice than emulsions with a droplet diameter of 20 nm. However, another report predicts that particles in the 10-200 nm size range can move faster and enter the lymphatic system and target immune cells more efficiently.