Abstract
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.
Highlights
The effectiveness of subunit vaccines relies on immunostimulatory adjuvants to induce potent and long-lasting antigen-specific immune responses
We have previously reported that OW-14, a low-cost emulsion adjuvant based on light mineral oil and foodgrade gum Arabic emulsifier, can stimulate high-level antigen-specific antibody responses in vaccines for swine influenza (SI), Mycoplasma hyopneumoniae, and classical swine fever (CSF) [16, 17]
According to dynamic light scattering (DLS) measurements, freshly prepared OWq emulsion adjuvant had nanoscale size of droplets with a mean value of approximately 200 nm and relatively low polydispersity, while emulsion prepared with oil-based adjuvant (OBA) had droplets around 320 nm with higher difference in droplet sizes (Table 1)
Summary
The effectiveness of subunit vaccines relies on immunostimulatory adjuvants to induce potent and long-lasting antigen-specific immune responses. Combination of the adjuvants with different modes of action presents potential on both enhanced and tailored immune responses for long-lasting protection against the disease. The combination of different immunostimulant substances, such as saponins, with emulsions and aluminum salts in vaccines for livestock has been actively studied by several research groups [5,6,7]. The addition of saponin extract Quil-A® to commercial emulsion-based vaccine was reported to improve humoral immune responses in pigs vaccinated for foot-and-mouth disease [7]. In this present study, we utilized saponin extract, as immunostimulatory compound and as emulsifier to stabilize the emulsion adjuvant
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