Early immune responses in skin and lymph node after skin delivery of Toll-like receptor agonists in neonatal and adult pigs

Sandra Vreman,Johanna M.J Rebel,Joanne Mccaffrey,Kristina Ledl,Ksenia Arkhipova,Damien Collins,Dennis Mcdaid,Huub F.J Savelkoul,Kerstin Skovgaard,Anne C Moore,Norbert Stockhofe-Zurwieden

doi:10.1016/j.vaccine.2021.02.028

Sandra Vreman, Johanna M.J Rebel + Show 9 more

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https://doi.org/10.1016/j.vaccine.2021.02.028

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The skin is potentially an important vaccine delivery route facilitated by a high number of resident antigen presenting cells (APCs), which are known to be stimulated by different Toll-like receptor agonists (TLRa). In this study, neonatal and adult pigs were vaccinated in the skin using dissolving microneedle patches to investigate the immuno-stimulatory potential of different TLRa and possible age-dependent differences early after vaccination. These patches contained TLR1/2a (Pam3Cys), TLR7/8a (R848) or TLR9a (CpG ODN) combined with inactivated porcine reproductive and respiratory syndrome virus (PRRSV) or with an oil-in-water stable emulsion. Vaccinated skin and draining lymph nodes were analysed for immune response genes using microfluidic high-throughput qPCR to evaluate the early immune response and activation of APCs. Skin pathology and immunohistochemistry were used to evaluate the local immune responses and APCs in the vaccinated skin, respectively. In both neonatal and adult pigs, skin vaccination with TLR7/8a induced the most prominent early inflammatory and immune cell responses, particularly in the skin. Skin histopathology and immunohistochemistry of APCs showed comparable results for neonatal and adult pigs after vaccination with the different TLRa vaccines. However, in vaccinated neonatal pigs in the skin and draining lymph node more immune response related genes were upregulated compared to adult pigs. We showed that both neonatal and adult skin could be stimulated to develop an immune response, particularly after TLR7/8a vaccination, with age-dependent differences in regulation of immune genes. Therefore, age-dependent differences in local early immune responses should be considered when developing skin vaccines.

Highlights

The skin is the largest organ in the body and forms a physical and immunological boundary to protect from injury and pathogens [1,2]
Neonatal and adult pigs were vaccinated with dissolving microneedle (DMN)-patches containing different TLR agonists (TLRa) in combination with Inactivated porcine reproductive and respiratory syndrome virus (iPRRSV)-antigen to investigate the immune-stimulatory potential of the TLRa and whether or not these immune responses were age-dependent
We compared the NV neonatal skin to the NV adult skin to investigate if differences in skin thickness, location and quantity of antigen presenting cells (APC) subsets or TLR expression were associated with the higher number of up-or downregulated genes in vaccinated neonatal skin compared to adult skin

Summary

Introduction

The skin is the largest organ in the body and forms a physical and immunological boundary to protect from injury and pathogens [1,2]. The epidermis and dermis are the most important layers that determine the immune responses within the skin [7,8]. These layers can be physically breached by dissolving microneedle (DMN)patches, a needle-free delivery system for skin vaccination [9], termed ‘‘microarray patches”. After vaccination, activated APCs mature and transport the vaccine-antigen to the draining lymph nodes (LNs), where the antigen is presented to naïve T cells [10,11] to induce an immune response. Besides APCs, epidermal keratinocytes and newly recruited dermal immune cells contribute to this skin vaccinated induced immune response [11,12]

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