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

Abstract Lung tissue-resident memory 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 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, lung, and spleen from AdNP-immunized or influenza x31-infected mice. We found that CD8+ TRM in the lungs of AdNP-immunized mice show increased homeostatic turnover and encounter persistent antigen in the lung. In addition, parabiosis experiments suggest that the influenza-specific CD8+ lung TRM pool is maintained in AdNP-immunized mice by continual recruitment of circulating TEM into the lung TRM pool. RNA-sequencing analysis comparing CD8+ lung 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. We are currently investigating how antigen is maintained in the lung following AdNP immunization using microscopy and Cre recombinase-expressing Adenovirus (AdCre) to identify antigen presenting cells harboring antigen long-term in the lung. The results of this study will identify mechanisms that improve the durability of cellular immunity, and will thus inform future design of cell-mediated influenza vaccines.