Persistent antigen can maintain lung resident memory CD8 T cells long-term

Abstract A sub-population of memory T cells, tissue resident memory T cells (TRM), have in recent years gained attention for their indispensable role in heterologous protection against respiratory viruses. For this reason, they are of great interest for vaccine research. However, the number of lung TRM decline within a few months after infection and researchers have been unable to determine how the TRM population, and protection, can be made to last long-term in the lung. We have previously shown that an Adenovirus expressing nucleoprotein (AdNP) from influenza A virus induce CD8 T cell mediated heterosubtypic immunity lasting up to at least 8 months post vaccination when administered locally and systemically, but the underlying reason was not investigated. Here, we show that the number of CD8 T cell in the lung induced by AdNP is significantly higher compared to cells induced by an influenza infection. Using AdNP, we show that CD8 TRM in the lung can be maintained for at least one year post-vaccination. Our results revealed that lung TRM continued to proliferate in-situ 8 months after AdNP vaccination. Importantly, this required pulmonary vaccination and antigen persistence in the lung, as non-respiratory vaccination routes failed to support lung TRM maintenance. Additionally, parabiosis experiments show that in AdNP vaccinated mice the lung TRM pool is sustained by continual replenishment from circulating memory CD8 T cells that differentiate into lung TRM, a phenomenon not observed in influenza infected parabiont partners. Concluding, these results demonstrates requirements for long-lived cellular immunity to influenza virus, knowledge that could be utilized in future vaccine design.