Single cell transcriptomics reveal the heterogeneities of TCR Vα7.2⁺CD161⁺ and TCR Vα7.2⁺CD161⁻ T cells in human peripheral blood

T cell receptor (TCR) usually determines the specificity and unique function of T cells. Recently, the unconventional T cells with a unique TCR have attracted great attentions because of their clinical importance. TCR Vα7.2⁺ cells, that consist of the CD161⁺ mucosal associated invariant T (MAIT) cells and CD161⁻ non-MAIT T cells, have been reported to play crucial roles in immune defenses. However, their characterizations in human blood are still obscure. This study aims to investigate the signatures and functions of circulating TCR Vα7.2⁺CD161⁺ MAIT and TCR Vα7.2⁺CD161⁻ cells under steady state.

The TCR Vα7.2⁺CD161⁺ and TCR Vα7.2⁺CD161⁻ cells were separately sorted from healthy donor peripheral blood mononuclear cells (PBMCs) and send for single cell RNA sequencing (scRNA-seq). Flow cytometry analysis was used to verify the findings obtained from scRNA-seq analysis.

Our findings demonstrated that there are more TCR Vα7.2⁺CD161⁺ cells than TCR Vα7.2⁺CD161⁻ cells in healthy donor PBMCs and revealed the differences between them. Under steady state, 4 TCR Vα7.2⁺CD161⁺ MAIT clusters existed in peripheral blood. Pseudotime analysis further implied the development trajectory of these MAIT cells, which was ordered from CCR7⁺ resting cluster to LGALS3⁺ transitional cluster, followed by KLRG1⁺ cluster and ending with CX3CR1⁺ terminally differentiated cytotoxic cluster. In addition, our results revealed that TCR Vα7.2⁺CD161⁻ cells consist of different kind of conventional T cells. These TCR Vα7.2⁺CD161⁻ non-MAIT cells showed a higher level of Granzyme B expression and upregulated genes associated with cytotoxicity, which implicated their roles in immune defense.

Our findings advanced the understandings of the evolution of circulating MAIT cells. We also preliminarily defined the TCR Vα7.2⁺CD161⁻ PBMCs as a combination of versatile CD4⁺ and CD8⁺ populations with cytotoxicity.