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

• Published in: Vaccine 2021-03, Vol.39 (13), p.1857-1869
• Main Authors: Vreman, Sandra, Rebel, Johanna M.J., McCaffrey, Joanne, Ledl, Kristina, Arkhipova, Ksenia, Collins, Damien, McDaid, Dennis, Savelkoul, Huub F.J., Skovgaard, Kerstin, Moore, Anne C., Stockhofe-Zurwieden, Norbert
• Format: Article
• Language: English
• Subjects: Adjuvant; Adults; Age; Agonists; Animal diseases; Animals; Antigen-presenting cells; Antigens; Biopsy; CpG islands; Experiments; Gene regulation; Genes; Histology; Histopathology; Hogs; Immune response; Immune system; Immunohistochemistry; Immunology; Inflammation; Lymph nodes; Lymphatic system; Microfluidics; Needles; Neonatal; Neonates; Newborn babies; Oligonucleotides; Receptors; Skin; Skin immunity; Skin vaccination; Swine; TLR1 protein; TLR7 protein; Toll-like receptor agonist; Toll-like receptors; Vaccines
• ISSN: 0264-410X; 1873-2518
• DOI: 10.1016/j.vaccine.2021.02.028

•The dermis of neonatal skin is thinner and contains more resident dermal macrophages compared to adult skin.•The number of resident skin dendritic cells in neonatal and adult skin is similar.•Toll-like receptor 7/8 agonists show potential as adjuvant for porcine skin vaccination in both age groups.•After vaccination, more early immune response related genes are regulated in neonatal skin than in adult skin. 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.