Background: Live-attenuated influenza vaccine (LAIV) was licensed for prophylaxis of children 2-17 years old in Europe in 2012 and is administered as a nasal spray. Live-attenuated influenza vaccine induces both mucosal and systemic antibodies and systemic T-cell responses. Tonsils are the lymph nodes serving the upper respiratory tract, acting as both induction and effector site for mucosal immunity.
Methods: Here, we have studied the early tonsillar T-cell responses induced in children after LAIV. Thirty-nine children were immunized with trivalent LAIV (containing A/H1N1, A/H3N2, and B viruses) at days 3, 7, and 14 before tonsillectomy. Nonvaccinated controls were included for comparison. Tonsils and peripheral blood (pre- and postvaccination) were collected to study T-cell responses.
Results: Tonsillar and systemic T-cell responses differed between influenza strains, and both were found against H3N2 and B viruses, whereas only systemic responses were observed against A/H1N1. A significant increase in cross-reactive tonsillar CD8+ T cells recognizing conserved epitopes from a broad range of seasonal and pandemic viruses occurred at day 14. Tonsillar T cells showed significant cytokine responses (Th1, Th2, and granulocyte-macrophage colony-stimulating factor).
Conclusions: Our findings support the use of LAIV in children to elicit broadly cross-reactive T cells, which are not induced by traditional inactivated influenza vaccines and may provide protection to novel virus strains.
Keywords: IFN-γ; LAIV; T cells; children; tonsils.
© The Author(s) 2020. Published by Oxford University Press for the Infectious Diseases Society of America.