Abstract

BackgroundVaccination is the principal strategy for prevention and control of diseases, and adjuvant use is an effective strategy to enhance vaccine efficacy. Traditional mineral oil-based adjuvants have been reported with post-immunization reactions. Developing new adjuvant formulations with improved potency and safety will be of great value.ResultsIn the study reported herein, a novel oil-in-water (O/W) Emulsion Adjuvant containing Squalane (termed EAS) was developed, characterized and investigated for swine influenza virus immunization. The data show that EAS is a homogeneous nanoemulsion with small particle size (~ 105 nm), low viscosity (2.04 ± 0.24 cP at 20 °C), excellent stability (at least 24 months at 4 °C) and low toxicity. EAS-adjuvanted H3N2 swine influenza vaccine was administrated in mice subcutaneously to assess the adjuvant potency of EAS. The results demonstrated that in mice EAS-adjuvanted vaccine induced significantly higher titers of hemagglutination inhibition (HI) and IgG antibodies than water-in-oil (W/O) vaccines or antigen alone, respectively, at day 42 post vaccination (dpv) (P < 0.05). EAS-adjuvanted vaccine elicited significantly stronger IgG1 and IgG2a antibodies and higher concentrations of Th1 (IFN-γ and IL-2) cytokines compared to the W/O vaccine or antigen alone. Mice immunized with EAS-adjuvanted influenza vaccine conferred potent protection after homologous challenge.ConclusionThe O/W emulsion EAS developed in the present work induced potent humoral and cellular immune responses against inactivated swine influenza virus, conferred effective protection after homologous virus challenge and showed low toxicity in mice, indicating that EAS is as good as the commercial adjuvant MF59. The superiority of EAS to the conventional W/O formulation in adjuvant activity, safety and stability will make it a potential veterinary adjuvant.

Highlights

  • Vaccination is the principal strategy for prevention and control of diseases, and adjuvant use is an effective strategy to enhance vaccine efficacy

  • Our results show that Emulsion Adjuvant containing Squalane (EAS)-adjuvanted H3N2 swine influenza vaccine can induce significantly higher antibody titers than Water in oil (W/O) vaccines in mice, and elicit a mixed Th1/Th2 response

  • Images from the O/W emulsion showed a characteristic spherical shape, and the diameter of emulsion droplets was in agreement with dynamic light scattering (DLS) measurements as described above

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Summary

Introduction

Vaccination is the principal strategy for prevention and control of diseases, and adjuvant use is an effective strategy to enhance vaccine efficacy. Traditional mineral oil-based adjuvants have been reported with post-immunization reactions. Traditional oil-based emulsion adjuvants, such as Freund’s complete or incomplete adjuvant, have been reported with post-immunization reactions. Previous studies demonstrate that commercial vaccines in a water-in-oil (W/ O) formulation is not highly effective in preventing vaccinated pigs from wild-type virus infection [5, 6]. Post-immunization reactions associated with mineral oil-based adjuvants have been reported, such as edema, abscess/granuloma formation or necrosis at injection sites, which render pork unfit for consumption and greatly limits the wide application of these vaccines [7]. Developing new adjuvant formulations with improved potency and safety will be of great value and impact both in the swine industry and for global public health. Swine influenza virus was used as a model antigen to investigate the new adjuvant’s immunogenicity

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