Tissue-resident memory T cells maintain identity after in vitro restimulation

Resident memory T (TRM) cells have been recently established as an important subset of memory cells that provide early and essential protection against reinfection in the absence of circulating memory T cells. Recent findings showing that TRM expand in vivo after repeated antigenic stimulation indicate that these memory T cells are not terminally differentiated. This suggest an opportunity for in vitro TRM expansion to apply in an immunotherapy setting. However, it has also been shown that TRM may not maintain their identity and form circulating memory T cells after in vivo restimulation. Therefore, we set out to determine how TRM respond to antigenic activation in culture. Using Listeria monocytogenes and LCMV infection models, we found that TRM from the intraepithelial compartment of the small intestine expand in vitro after antigenic stimulation and subsequent resting in homeostatic cytokines. A large fraction of the expanded TRM retained their phenotype, including the expression of key TRM markers CD69 and CD103 (ITGAE). Optimal culture of TRM required low O2 pressure to maintain the expression of these and other TRM associated molecules. Expanded TRM retained their effector capacity to produce cytokines after restimulation, but did not acquire a highly glycolytic profile indicative of effector T cells. Proteomic analysis confirmed TRM profile retention, including expression of TRM-related transcription factors, tissue retention factors, adhesion molecules and enzymes involved in fatty acid metabolism. Collectively, our data indicate that limiting oxygen conditions support in vitro expansion of TRM cells that maintain their TRM phenotype, at least in part, suggesting an opportunity for therapeutic strategies that require in vitro expansion of TRM.