Activation and Induction of Antigen-Specific T Follicular Helper Cells Play a Critical Role in Live-Attenuated Influenza Vaccine-Induced Human Mucosal Anti-influenza Antibody Response

There is increasing interest recently in developing intranasal vaccines against respiratory tract infections. The antibody response is critical for vaccine-induced protection, and T follicular helper cells (T-FH) are considered important for mediating the antibody response. Most data supporting the role for T-FH in the antibody response are from animal studies, and direct evidence from humans is limited, apart from the presence of T-FH-like cells in blood. We studied the activation and induction of T-FH and their role in the anti-influenza antibody response induced by a live-attenuated influenza vaccine (LAIV) in human nasopharynx-associated lymphoid tissue (NALT). T-FH activation in adenotonsillar tissues was analyzed by flow cytometry, and anti-hemagglutinin (anti-HA) antibodies were examined following LAIV stimulation of tonsillar mononuclear cells (MNC). Induction of antigen-specific T-FH by LAIV was studied by flow cytometry analysis of induced T-FH and CD154 expression. LAIV induced T-FH proliferation, which correlated with anti-HA antibody production, and T-FH were shown to be critical for the antibody response. Induction of T-FH from naive T cells by LAIV was shown in newly induced T-FH expressing BCL6 and CD21, followed by the detection of anti-HA antibodies. Antigen specificity of LAIV-induced T-FH was demonstrated by expression of the antigen-specific T cell activation marker CD154 upon challenge by H1N1 virus antigen or HA. LAIV-induced T-FH differentiation was inhibited by BCL6, interleukin-21 (IL-21), ICOS, and CD40 signaling blocking, and that diminished anti-HA antibody production. In conclusion, we demonstrated the induction by LAIV of antigen-specific T-FH in human NALT that provide critical support for the anti-influenza antibody response. Promoting antigen-specific T-FH in NALT by use of intranasal vaccines may provide an effective vaccination strategy against respiratory infections in humans. IMPORTANCE Airway infections, such as influenza, are common in humans. Intranasal vaccination has been considered a biologically relevant and effective way of immunization against airway infection. The vaccine-induced antibody response is crucial for protection against infection. Recent data from animal studies suggest that one type of T cells, T-FH, are important for the antibody response. However, data on whether T-FH-mediated help for antibody production operates in humans are limited due to the lack of access to human immune tissue containing T-FH. In this study, we demonstrate the induction of T-FH in human immune tissue, providing critical support for the anti-influenza antibody response, by use of an intranasal influenza vaccine. Our findings provide direct evidence that T-FH play a critical role in vaccine-induced immunity in humans and suggest a novel strategy for promoting such cells by use of intranasal vaccines against respiratory infections.