Evaluation of the immune response induced by intradermal vaccination by using a needle-less system in comparison with the intramuscular route in conventional pigs

The immune response induced by intradermal vaccination using a needle-less device was evaluated in conventional pigs in comparison with the more conventional intramuscular vaccination; to this purpose, vaccination against Aujeszky’s Disease (AD) was used as a model of antiviral immunity. Two groups of pigs (n = 10 each) were vaccinated 4 weeks apart respectively by the intramuscular (IM group) and intradermal route (ID group; needle-less I.D.A.L.® vaccinator) with an AD modified live virus. Ten pigs injected with the vaccine adjuvant only were kept as sham-vaccinated controls (C group).On blood samples collected at 0, 2, 4, 5, 6 and 7 weeks post-vaccination (PV) ADV-specific virus neutralizing (VN) antibodies, IFN-γ secreting cells (SC), lymphocyte subsets and IFN-γ gene expression in PBMC were evaluated.VN antibodies increased after the 1st vaccination and peaked after the 2nd vaccination in both vaccinated groups. Also IFN-γ SC reached maximum levels in both groups after administration of the booster dose. Pigs in the control group remained negative for both parameters throughout the study. Flow cytometry showed persistently higher levels of CD3−CD8α+ Natural Killer cells in both vaccinated pigs. The ID group showed an earlier and regulated activation characterized by an increase of cytotoxic CD8β+ T lymphocytes and CD25+ cells after the boosting dose. No statistically significant differences between treated and control groups were detected for memory CD4+CD8α+low T cells. Upregulation of IFN-γ gene expression in PBMC was detected in ID and IM pigs after both vaccine administrations, although at a different extent. Overall, the results showed that the intradermal vaccine delivery by a needle-less device can prime a strong humoral and cellular immune response comparable to that obtained by the intramuscular vaccination.