Persistent Antigen Harbored by Alveolar Macrophages Enhances the Maintenance of Lung-Resident Memory CD8⁺ T Cells

Lung tissue-resident memory T cells are crucial mediators of cellular immunity against respiratory viruses; however, their gradual decline hinders the development of T cell-based vaccines against respiratory pathogens. Recently, studies using adenovirus (Ad)-based vaccine vectors have shown that the number of protective lung-resident CD8 + T RMs can be maintained long term. In this article, we show that immunization of mice with a replication-deficient Ad serotype 5 expressing influenza (A/Puerto Rico/8/34) nucleoprotein (AdNP) generates a long-lived lung T RM pool that is transcriptionally indistinct from those generated during a primary influenza infection. In addition, we demonstrate that CD4 + T cells contribute to the long-term maintenance of AdNP-induced CD8 + T RMs. Using a lineage tracing approach, we identify alveolar macrophages as a cell source of persistent NP Ag after immunization with AdNP. Importantly, depletion of alveolar macrophages after AdNP immunization resulted in significantly reduced numbers of NP-specific CD8 + T RMs in the lungs and airways. Combined, our results provide further insight to the mechanisms governing the enhanced longevity of Ag-specific CD8 + lung T RMs observed after immunization with recombinant Ad.