Identifying mechanisms that enhance the longevity of tissue-resident memory CD8+ T cells in the lung

Abstract Lung tissue-resident memory CD8+ T cells (TRM) are crucial mediators of cellular immunity against influenza viruses, but the number of these cells in the lung tissue gradually declines in the months following influenza infection. Recently, we showed that intranasal immunization with a replication-deficient adenovirus that expresses the nucleoprotein from influenza A virus (AdNP) results in long-term maintenance of lung CD8+ TRM for up to 1-year post-immunization. However, the mechanism(s) that promote this enhanced longevity of FluNP-specific CD8+ lung TRM remain unknown. Using a combination of mouse infection models, flow cytometry, and RNA-sequencing, we compared CD8+ T cells from the airways, lungs, and spleen of AdNP-immunized or influenza x31-infected mice. We found that CD8+ TRM in the lungs of AdNP-immunized mice show increased homeostatic turnover and hallmarks of persistent antigen stimulation in the lung. However, RNA-sequencing analysis comparing lung CD8+ TRM from AdNP-immunized and x31-infected mice at 1-month and 1-year post-immunization showed only minor variations that did not fully explain the differences in lung TRM persistence. Lineage tracing experiments using a Cre recombinase-expressing Adenovirus (AdCre) identified alveolar macrophages as the primary cell type harboring persistent antigen in the lung. Together, these results define one mechanism for enhancing the durability of lung TRM, which is an important consideration for the design of future cell-mediated influenza vaccines