Protective function and durability of mouse lymph node-resident memory CD8(+) T cells

Protective lung tissue-resident memory CD8(+)T cells (Trm) form after influenza A virus (IAV) infection. We show that IAV infection of mice generates CD69(+)CD103(+)and other memory CD8(+)T cell populations in lung-draining mediastinal lymph nodes (mLNs) from circulating naive or memory CD8(+)T cells. Repeated antigen exposure, mimicking seasonal IAV infections, generates quaternary memory (4M) CD8(+)T cells that protect mLN from viral infection better than 1M CD8(+)T cells. Better protection by 4M CD8(+)T cells associates with enhanced granzyme A/B expression and stable maintenance of mLN CD69(+)CD103(+)4M CD8(+)T cells, vs the steady decline of CD69(+)CD103(+)1M CD8(+)T cells, paralleling the durability of protective CD69(+)CD103(+)4M vs 1M in the lung after IAV infection. Coordinated upregulation in canonical Trm-associated genes occurs in circulating 4M vs 1M populations without the enrichment of canonical downregulated Trm genes. Thus, repeated antigen exposure arms circulating memory CD8(+)T cells with enhanced capacity to form long-lived populations of Trm that enhance control of viral infections of the mLN.