Double-negative T resident memory cells of the lung react to influenza virus infection via CD11c(hi) dendritic cells.

Immunity to Influenza A virus (IAV) is controlled by conventional TCRαß(+) CD4(+) and CD8(+) T lymphocytes, which mediate protection or cause immunopathology. Here, we addressed the kinetics, differentiation, and antigen specificity of CD4(-)CD8(-) double-negative (DN) T cells. DNT cells expressed intermediate levels of TCR/CD3 and could be further divided in γδ T cells, CD1d-reactive type I NKT cells, NK1.1(+) NKT-like cells, and NK1.1(-) DNT cells. NK1.1(-) DNT cells had a separate antigen-specific repertoire in the steady-state lung, and expanded rapidly in response to IAV infection, irrespectively of the severity of infection. Up to 10% of DNT cells reacted to viral nucleoprotein. Reinfection experiments with heterosubtypic IAV revealed that viral replication was a major trigger for recruitment. Unlike conventional T cells, the NK1.1(-) DNT cells were in a preactivated state, expressing memory markers CD44, CD11a, CD103, and the cytotoxic effector molecule FasL. DNT cells resided in the lung parenchyma, protected from intravascular labeling with CD45 antibody. The recruitment and maintenance of CCR2(+) CCR5(+) CXCR3(+) NK1.1(-) DNT cells depended on CD11c(hi) dendritic cells (DCs). Functionally, DNT cells controlled the lung DC subset balance, suggesting they might act as immunoregulatory cells. In conclusion, we identify activation of resident memory NK1.1(-) DNT cells as an integral component of the mucosal immune response to IAV infection.

Natural and long-lasting cellular immune responses against influenza in the M2e-immune host.

Influenza is a global health concern. Licensed influenza vaccines induce strain-specific virus-neutralizing antibodies but hamper the induction of possibly cross-protective T-cell responses upon subsequent infection.(1) In this study, we compared protection induced by a vaccine based on the conserved extracellular domain of matrix 2 protein (M2e) with that of a conventional whole inactivated virus (WIV) vaccine using single as well as consecutive homo- and heterosubtypic challenges. Both vaccines protected against a primary homologous (with respect to hemagglutinin and neuraminidase in WIV) challenge. Functional T-cell responses were induced after primary challenge of M2e-immune mice but were absent in WIV-vaccinated mice. M2e-immune mice displayed limited inducible bronchus-associated lymphoid tissue, which was absent in WIV-immune animals. Importantly, M2e- but not WIV-immune mice were protected from a primary as well as a secondary, severe heterosubtypic challenge, including challenge with pandemic H1N1 2009 virus. Our findings advocate the use of infection-permissive influenza vaccines, such as those based on M2e, in immunologically naive individuals. The combined immune response induced by M2e-vaccine and by clinically controlled influenza virus replication results in strong and broad protection against pandemic influenza. We conclude that the challenge of the M2e-immune host induces strong and broadly reactive immunity against influenza virus infection.