Scientist Earle A. Chiles Res. Inst., Providence Cancer Inst., Oregon, United States
Introduction/Rationale: Blockade of NKG2A/HLA-E interaction is a promising strategy to unleash the anti-tumor response; but the capacity of NKG2A+ CD8 T cells to recognize the tumor as yet to be demonstrated. Furthermore, the nature of the signals driving NKG2A expression requires clarification.
Methods: To better characterize NKG2A-expressing CD8 T cells in human solid tumors, we analyzed their phenotype in mismatch repair proficient (MMR-p) colorectal cancer (CRC) and head and neck squamous cell carcinoma (HNSCC) by flow cytometry. We also performed scRNA-seq, TCR repertoire analysis and antigen reactivity experiments to determine their differentiation in the tumor and evaluate their capacity to recognize tumor antigens. Finally, we investigated the signals leading to the induction of NKG2A on naïve CD8 T cells
Results: NKG2A was expressed by 10 to 15% of tumor-infiltrating CD8 T cells (CD8 TIL), with the dominant population co-expressing CD39 and CD103 (DP CD8), a phenotype associated with tumor-reactive T cells. Analysis of our scRNA-seq revealed that NKG2A was induced in the tumor microenvironment as cells differentiate into DP CD8 TILs and its expression was the highest on cells with high cytotoxic potential. This developmental trajectory resulted in a high degree of overlap between the TCR repertoires of NKG2A- and NKG2A+ DP CD8 TILs and those cells displayed shared tumor antigen specificities. We also showed that, while TCR stimulation together with TGF-β was not sufficient to induce NKG2A on naïve CD8 T cells, IL-12 was essential for its expression. In response to SEB, we demonstrated that both CD4 T cells and APCs were required for NKG2A upregulation, and this mechanism was controlled by CD40/CD40L interaction and IL-12 secretion.
Conclusion: Altogether, our work revealed that NKG2A, an inhibitory receptor, can be induced in human tumor-reactive CD8 T cells by IL-12 in a TGF-β-rich environment, demonstrating a previously unappreciated immune-regulatory feedback loop following IL-12 stimulation.
