Non-invasive aerosol application, sprayed directly into mouse airways with Penn-Century MicroSprayer was performed for pulmonary immunization. 40 µg of DNA were complexed with in vivo-jetPEI at a N/P ratio of 7.5 in a final volume of 50 µl. This represents an efficient approach for inducing robust pulmonary CD8+ T-cell populations that are effective at protecting against respiratory pathogens.

Vaccination strategies for protection against a number of respiratory pathogens must induce T-cell populations in both the pulmonary airways and peripheral lymphoid organs. In this study, we show that pulmonary immunization using plasmid DNA formulated with the polymer polyethyleneimine (PEI-DNA) induced antigen-specific CD8(+) T cells in the airways that persisted long after antigen local clearance. The persistence of the cells was not mediated by local lymphocyte proliferation or persistent antigen presentation within the lung or airways. These vaccine-induced CD8(+) T cells effectively mediated protective immunity against respiratory challenges with vaccinia virus and influenza virus. Moreover, this protection was not dependent upon the recruitment of T cells from peripheral sites. These findings demonstrate that pulmonary immunization with PEI-DNA is an efficient approach for inducing robust pulmonary CD8(+) T-cell populations that are effective at protecting against respiratory pathogens.