Identification and characterization of tissue resident memory T cells in malignant pleural effusions associated with non-small cell lung cancer.

Tissue resident memory T cells (TRM) play a critical role in cancer immunity and their presence in solid tumors is associated with improved prognosis and response to therapy. Although TRM have been identified and their function characterized in lung cancers, little is known regarding TRM outside of a tissue context, such as within malignant pleural effusions (MPE). As MPE are routinely drained and collected to manage symptoms, analysis of this fluid can provide an insight into the peri-tumoral environment. In this study, we performed flow cytometry and single cell RNAseq (scRNAseq) on MPE associated with non-small lung cancer and examined the phenotype and function of TRM. We found that 14% of CD8+ T cells and 6% of CD4+ T cells were TRM, as defined by the phenotype of CD45RO+CCR7-CD62L- and expressing 1 or both of CD69 and CD103. The scRNAseq revealed distinct clusters expressing TRM-associated genes including ITGAE and CD49A and lacking expression of SELL, CCR7, and IL7RA. TRM did not differ from other memory T cell subsets, such as T central memory (TCM) and T effector memory (TEM) cells, in expression of the inhibitory markers PD-1, TIGIT, and CD39. When TRM function was assessed by measuring the production of IFN-γ, TNF-α, and CD107a after stimulation with αnti-CD3 antibodies in vitro, TRM had comparable function to T effector cells (TE), indicating that despite expression of exhaustion markers these cells retained effector function. Finally, we found that CD69 expression, and not CD103 expression, on TRM was associated with production of effector cytokines.