Food-Grade Saponin Extract as an Emulsifier and Immunostimulant in Emulsion-Based Subunit Vaccine for Pigs.

Subunit vaccines consisting of highly purified antigens require the presence of adjuvants to create effective and long-lasting protective immunity. Advances on adjuvant research include designing combination adjuvants which incorporate two or more adjuvants to enhance vaccine efficacy. Previously, an oil-in-water emulsion adjuvant (OW-14) composed of mineral oil and an inexpensive gum Arabic emulsifier has been reported demonstrating enhanced and robust immune responses when used as an adjuvant in swine subunit vaccines. This study presents a modified version of OW-14 prepared with food-grade Quillaja saponin extract (OWq). In new OWq emulsion, saponin extract served as an emulsifier for stabilization of emulsion droplets and as an immunoactive compound. The use of saponins allowed to reduce the required amount of emulsifier in the original OW-14. However, emulsion stabilized with saponins demonstrated extended physical stability even at elevated temperature (37°C). The two-dose vaccination with a classical swine fever virus (CSFV) glycoprotein E2-based vaccine formulated with OWq produced higher levels of E2-specific IgG and virus neutralizing antibodies in pigs in contrast with animals that received the vaccine adjuvanted with oil only. In addition, new OWq adjuvant was safe to use in the vaccination of pigs.

Immunomodulatory and physical effects of phospholipid composition in vaccine adjuvant emulsions.

Egg phosphatidylcholine is commonly used as an emulsifier in formulations administered parenterally. However, synthetic phosphatidylcholine (PC) emulsifiers are now widely available and may be desirable substitutes for egg-derived phospholipids due to stability, purity, and material source considerations. In earlier work, we demonstrated that a squalene-1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) emulsion provided equivalent physical stability compared to a squalene-egg PC emulsion. In the present manuscript, we evaluate the physical stability of vaccine adjuvant emulsions containing a range of other synthetic phosphatidylcholine emulsifiers. Besides the POPC emulsion, the 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) emulsion showed good particle size and visual stability compared to emulsions made with other synthetic phospholipids. Moreover, comparable immune responses were elicited by squalene emulsions employing various synthetic PC or egg PC emulsifiers in combination with an inactivated influenza vaccine or a recombinant malaria antigen, and these responses were generally enhanced compared to antigen without adjuvant. Therefore, we show that (1) some synthetic PCs (DMPC, POPC, and to a lesser extent 1,2-dioleoyl-sn-glycero-3-phosphocholine) are effective stabilizers of squalene emulsion over a range of storage temperatures while others are not (1,2-distearoyl-sn-glycero-3-phosphocholine, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine, and 1,2-dilauroyl-sn-glycero-3-phosphocholine) and (2) the immunogenicity of stable squalene emulsions is similar regardless of PC source.