Dynamic equilibrium of lung Trm dictates waning immunity after IAV infection

Lung resident memory (Trm) CD8 T cells induced by influenza A virus (IAV), are pivotal for providing heterosubtypic immunity, but are not maintained long term, causing gradual loss of protection. This contrasts sharply with long-term maintenance of Trm induced by localized infections of the skin and other tissues. Here we show that the decline in lung Trm is determined by an imbalance between apoptosis and lung recruitment/conversion to Trm of circulating memory cells. At the cellular level, circulating effector memory (Tem) rather than central memory (Tcm) cells are the precursors for conversion to lung Trm. Time-dependent changes in expression of genes critical for Trm differentiation together with enrichment of Tcm diminish the capacity of circulating memory CD8 T cells to form Trm, explaining why IAV-induced Trm are not stably maintained over time. Importantly, systemic booster immunization, through increasing the number of circulating Tem cells, induces an increase in lung Trm pool, providing a new rational for future IAV vaccines. Two treatment groups + naive control group. Treatment groups: 5 samples, each one represents an RNA pooled from 5 individual mice. Naive control: 3 samples, each one preresents RNA from individual naive P14 transgenic mouse. This series contains data only for the two treatment groups.