Immune responses induced by inactivated porcine reproductive and respiratory syndrome virus (PRRSV) vaccine in neonatal pigs using different adjuvants

Sandra Vreman,Norbert Stockhofe-Zurwieden,Ditta J Popma-De Graaf,Huub F.J Savelkoul,C Barnier-Quer,N Collin,Damien Collins,Dennis Mcdaid,Anne C Moore,Johanna M.J Rebel

doi:10.1016/j.vetimm.2020.110170

Abstract

Vaccination of neonatal pigs could be supportive to prevent porcine reproductive and respiratory syndrome virus (PRRSV), which is an important porcine pathogen causing worldwide welfare and health problems in pigs of different age classes. However, neonatal immunity substantially differs to adults, thus different vaccines may be required in neonateal pigs. We examined if the immunogenicity and efficacy of inactivated PRRSV (iPRRSV) vaccines in neonatal pigs could be improved with adjuvants containing oil-in water (O/W) emulsions with or without Toll-like receptor (TLR) agonists and by altering the delivery route from intramuscular (i.m.) to the skin. Three-day-old PRRSV-naïve piglets (n = 54, divided in 6 groups) received a prime vaccination and a booster vaccination four weeks later. The vaccine formulations consisted of different O/W emulsions (Montanide™ ISA28RVG (ISA28)), a squalene in water emulsion (SWE) for i.m. or a Stable Emulsion (SE) with squalene for skin vaccination) and/or a mixture of TLR1/2, 7/8 and 9 agonists (TLRa) combined with iPRRSV strain 07V063. These vaccines were delivered either i.m. (ISA28, SWE, TLRa or SWE + TLRa) or into the skin (skiSE + TLRa) with dissolving microneedle (DMN)-patches. All animals received a challenge with homologous PRRSV three weeks after booster vaccination. Specific antibodies, IFN-γ production and viremia were measured at several time-points after vaccination and/or challenge, while lung pathology was studied at necropsy. After booster vaccination, only ISA28 induced a specific antibody response while a specific T-cell IFN-γ response was generated in the SWE group, that was lower for ISA28, and absent in the other groups. This suggests that prime vaccination in neonates induced a specific immune response after booster vaccination, dependent on the emulsion formulation, but not dependent on the presence of the TLRa or delivery route. Despite the measured immune responses none of the vaccines showed any efficacy. Further research focused on the early immune response in draining lymph nodes is needed to elucidate the potential of TLR agonists in vaccines for neonatal pigs.

Highlights

Porcine reproductive and respiratory syndrome virus (PRRSV) is occurring globally causing health and welfare problems with severe economic losses (Holtkamp et al, 2013; Nathues et al, 2017)
After 1 h of incubation, cells were stimulated with the same Toll-like receptor (TLR) agonists as used in the vaccine adjuvant: TLR1/2 agonist (10 μg/mL Pam3Cys L2000 from EMC microcollections), TLR7/8 agonist (5 μg/mL R848, Resiquimod from Inviv oGen), TLR9 agonist (5 μg/mL CpG ODN-type A sequence D32, 5′ggTGCGTCGACGCAGggggg-3′, from Eurofins Genomics.), the TLR1/2a, 7/8 and 9 agonist mixture, the TLR1/2 and 9 agonist mixture (10 μg/mL and 5 μg/ mL, respectively) or cells were left unstimulated as negative control
The TLR1/2 + 7/8 + 9 agonist combination stimulated neonateal PBMC to produce significant levels of IFN- γ, IL12p40, IL-4, IL-1β, IL-6 and IL-10 compared to unstimulated control samples and the TLR1/2 agonist showed minimal potential to induce cytokine production compared to the TLR7/8 and 9 agonists

Summary

Introduction

Porcine reproductive and respiratory syndrome virus (PRRSV) is occurring globally causing health and welfare problems with severe economic losses (Holtkamp et al, 2013; Nathues et al, 2017) This positive-stranded RNA virus of the Arteriviridae causes abortions in sows, respiratory diseases and increased susceptibility to other infections in nursery and fattening pigs. Milk-derived maternal antibodies (Poonsuk and Zimmer man, 2017), could interfere with the development of an active immune response in different ways (Chappuis, 1998; Siegrist, 2003; Zinkernagel, 2003). All these aspects could complicate iPRRSV vaccination of neonatal pigs. New adjuvants and adjuvant formulations could enhance the immunogenicity of inactivated vaccines, but must be suitable for the neonatal immune system (Kollmann and Marchant, 2016; Mohr and Siegrist, 2016)

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Conclusion