Identification and characterization of a dominated T cell population in tumor associated antigen specific CD8+T cells of tumor microenvironment

Abstract The characteristics and roles of tumor associated antigens (TAAs) specific tumor infiltrative T cells (TILs) are not well understood. Alpha-enolase is one TAA of oral squamous cell carcinoma (OSCC) and pancreatic cancer, and are highly expressed in many cancer types by analyzing the TCGA database. We detected α-enolase responsive CD8 +T cells in peripheral blood mononuclear cells (PBMCs) and TILs of OSCC patients. The α-enolase responsive CD8 +T cells significantly increased in TILs than those in PBMCs. We developed two tetramers to identify two different α-enolase peptides specific CD8 +T cells. Two types of tetramer positive CD8 +TILs, total CD8 +TILs, and total CD8 +T cells from PBMC of three OSCC patients were sorted. Single cell RNA sequencing was performed. Unbiased clustering revealed 11 distinct CD8 +T cell clusters. To our surprise, the cell population patterns of both tetramer positive CD8 +TILs were similar, but were much different from total blood CD8 +T cells or total CD8 +TILs. The percentages of relatively exhausted T cells were similar in three TIL groups, but was nearly absent in blood. The blood CD8 +T cells had the highest percentage of effector memory T cells and naïve T cells. A specific cell cluster dominated (>50% population) in the two tetramer positive CD8 +TILs. The expression of important immune related genes in the specific cell cluster were all relatively low. That hinted this T cell subset was more quiescent than other cell clusters, and may have potentials to be activated. Further clarify the roles of the special T cell subset in tumor immunology is warranted. Supported by grants from National Science and Technology Council, Taiwan (110-2314-B-002-299)