Elsevier

Vaccine

Volume 36, Issue 12, 14 March 2018, Pages 1606-1613
Vaccine

Intradermal immunization with inactivated swine influenza virus and adjuvant polydi(sodium carboxylatoethylphenoxy)phosphazene (PCEP) induced humoral and cell-mediated immunity and reduced lung viral titres in pigs

https://doi.org/10.1016/j.vaccine.2018.02.026Get rights and content

Abstract

Swine influenza virus is endemic worldwide and it is responsible for significant economic losses to the swine industry. A vaccine that stimulates a rapid and long-lasting protective immune response to prevent this infection is highly sought. Poly[di(sodium carboxylatoethylphenoxy)-phosphazene (PCEP) has demonstrated adjuvant activity when formulated as part of multiple vaccines in mice and pigs. In this study we examined the magnitude and type of immune response induced in pigs vaccinated via the intramuscular or intradermal routes with inactivated swine influenza virus (SIV) H1N1 vaccine formulated with PCEP. Intradermal administration of PCEP-adjuvanted inactivated SIV vaccine stimulated significant anti-SIV antibody titres, increased neutralizing antibodies, and significantly reduced lung virus load with limited reduction of gross lung lesions after challenge with virulent H1N1 relative to control animals. These results indicate that PCEP may be effective as a vaccine adjuvant against swine influenza viruses in pigs and should be considered a potential candidate adjuvant for future swine intradermal influenza vaccines.

Introduction

Swine influenza A virus (SIV) causes influenza, a highly contagious acute respiratory disease of pigs responsible for significant economic losses to the swine industry. In addition, SIV infections are a threat to public health since transmission from pigs to humans can occur. There has been an increase in genetic diversity of swine influenza A virus (SIV) in North America over the last two decades but the majority of the SIV infections in pigs are caused by subtypes H1N1, H1N2 and H3N2 [1]. The most cost-effective biomedical approach to control SIV infection is through effective vaccination of pigs with current vaccines comprised of inactivated H3N2 and H1N1 [2]. Reformulation of the vaccine to include a potent adjuvant may improve the efficacy of existing SIV vaccines.

Adjuvants are routinely included in vaccines comprised of inactivated virus and/or subunit vaccines to augment the magnitude and quality of immune responses and by enhancing onset and extending duration of immunity. Polyphosphazene adjuvants are high-molecular weight, water-soluble polymers that, when co-administered with many viral and bacterial antigens, have been shown to enhance long-lasting immune responses [3], [4], [5], [6] and robust Th1/Th2 type, broad spectrum immune responses in mice [7] and are potent adjuvants for intradermal immunization in pigs [8], [9]. PCEP regulates a number of “immune response genes” when administered intradermally and may promote a Th-2 type immune response [10].

In this study, we evaluate the immunogenicity and protective efficacy of PCEP-adjuvanted inactivated SIV vaccine in pigs. We show that PCEP may be effective as a vaccine adjuvant capable of generating neutralizing antibodies against swine influenza viruses in pigs as well as reduce viral load after challenge and should be considered as a a candidate for future intradermal swine influenza vaccines.

Section snippets

Swine influenza virus adsorption, purification and inactivation

Confluent Madin-Darby canine kidney (MDCK) cells (T-75 flasks) were inoculated with a Saskatchewan isolate influenza swine H1N1 virus (A/SW/SK 02 H1N1 (H1N1)) at an M.O.I. of 0.001 for 1 h with minimal essential medium (MEM) (Sigma-Aldrich, Oakville, ON, CAN), which was then supplemented with 0.2% BSA (Sigma-Aldrich, Oakville, ON, CAN), 1 μg/mL TPCK-trypsin (MJSBioLynx, Brockville, ON, CAN) and 50 μg/mL gentamicin. Cultures were incubated in a humidified 5% CO2 atmosphere at 37 °C for 3 days or

Immune responses after vaccination with live inactivated H1N1 swine influenza virus vaccine formulated with PCEP adjuvant

Pigs were injected through the intradermal (ID) route with PBS or with inactivated SIV (128, 256, 512 and 1024 HAU) ± 500 μg PCEP) then boosted 21 days later. Serum samples were collected over a period of 36 days and antigen-specific serum antibody titres were assayed by ELISA. Negligible antibody titres were detected in piglets immunized with inactivated SIV alone or in the presence of adjuvants 21 days after immunization which suggests that the primary response was not very robust (Fig. 1).

Discussion

Vaccination is the most efficient method of protection against influenza infections [2], [19] but the rapidly mutating virus makes it necessary to develop new influenza vaccines annually [20]. Pigs can become infected with influenza viruses from birds, humans or other hosts and thus they act as a ‘mixing vessel where influenza genes from different strains can reassert to develop into a novel influenza virus not recognized by the immune system. Thus, the new influenza virus can be easily

Acknowledgements

Financial support for this work was provided by Saskatchewan Agriculture Development Fund, Canada and Alberta Livestock and Meat Agency, Canada. We greatly appreciate the technical assistance with animal experiments from the animal care personnel at VIDO-InterVac and Donna Dent’s technical expertise with the ELISAs. H.L.W. is an adjunct professor in the Department of Veterinary Microbiology and the School of Public Health at the University of Saskatchewan and acting Program Manager for the

References (32)

  • W. Keitel et al.

    Dose ranging of adjuvant and antigen in a cell culture H5N1 influenza vaccine: safety and immunogenicity of a phase 1/2 clinical trial

    Vaccine

    (2010)
  • Y. Lin et al.

    Interleukin-17 is required for T helper 1 cell immunity and host resistance to the intracellular pathogen Francisella tularensis

    Immunity

    (2009)
  • J.S. Rathore et al.

    Protective role of Th17 cells in pulmonary infection

    Vaccine

    (2016)
  • A. Vincent et al.

    Review of influenza A virus in swine worldwide: a call for increased surveillance and research

    Zoonoses Public Health

    (2014)
  • E. Thacker et al.

    Swine influenza virus: zoonotic potential and vaccination strategies for the control of avian and swine influenzas

    J Infect Dis

    (2008)
  • N.F. Eng et al.

    PCEP enhances IgA mucosal immune responses in mice following different immunization routes with influenza virus antigens

    J Immune Therapies Vacc

    (2010)
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    These authors contributed equally to this research.

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