CCR5-mediated dynamic maintenance of resident memory T cells in the respiratory tract

Tissue-resident memory T cells (T_RM) play a key role in defense against pathogen invading barrier sites and other non-lymphoid tissues. How T_RM cells are maintained in various tissues, and how they relate to antigen-experienced memory T cells in lymphoid organs are not fully understood. By barcode-based lineage tracing and single-cell transcriptome analysis, we found a distinct population of CD69⁺CD103⁺ virus-specific CD8⁺ T cells in draining lymph nodes (dLNs) following intranasal influenza infection. Intriguingly, these dLN T_RM cells and lung T_RM cells shared similar function-neutral barcode contents and transcriptomic features, implicating local circulation between the lung and dLNs in the maintenance of resident memory. Ablation of CXCR3 from CD8⁺ T cells, which impairs lung T_RM generation, severely reduced the abundance of dLN T_RM cells, suggesting that dLN T_RM cells are connected to lung T_RM cells by retrograde migration. Our screen for chemokines and chemokine receptors implicated the CCR5-CCL5 axis in promoting lung-to-dLN migration. Temporary CCR5 blockade by intratracheal administration of Maraviroc, a CCR5 inhibitor, reduced the abundance of dLN T_RM cells without affecting lung T_RM cells. By intratracheal cell transfer, CCR5-deficient CD8⁺ T cells were found impaired in lung-to-dLN migration. Finally, dLN T_RM cells actively participated in the secondary response and could reconstitute lung T_RM cells following influenza infection. Our results support a model in which lung-to-dLN TRM retrograde migration helps maintain the CD8⁺ memory resident in the respiratory tract and optimizes the local T-cell response to reinfection.