Abstract A198: The inhibitory checkpoint molecule NKG2A is upregulated on tumor-infiltrating NK cells and CD8 T-cells in human head and neck tumors

Background: Immunotherapy has revolutionized cancer therapy by targeting checkpoint molecules found on endogenous immune cells. Presently, the most commonly targeted checkpoint molecules are CTLA-4 and PD-1, which results in response rates of approximately 25% in head and neck squamous cell carcinomas (HNSCC). To improve treatment, additional immune checkpoint molecules expressed in the tumor microenvironment must be identified. Natural Killer Group 2 A (NKG2A) is an inhibitory receptor found on NK cells and CD8 T-cells, the receptor for which is HLA-E, a non-classical MHC molecule often overexpressed in solid tumors. This study aimed to identify if NKG2A is expressed on tumor infiltrating NK cells and CD8 T-cells from human HNSCC tumors as it is a potential therapeutic target. Methods: Fresh human HNSCC tumors were digested with Miltenyi Human Tumor Dissociation Kit and Gentle Macs machine following manufacturers’ instructions. Cells were then stained for surface phenotyping or frozen for functional assays. Results: We analyzed and compared tumor-infiltrating NK cells and CD8 T-cells from HNSCC patients with matched PBMC by flow cytometry for the expression of activating and inhibitory receptors. We found a unique population of effector memory PD-1+ NKG2A+ CD8 T-cells which was absent from the blood. NKG2A+ PD-1+ CD8 T-cells expressed higher levels of CTLA-4 and LAG3 as well as produced lower IFN-γ than NKG2A- PD-1+ CD8 T-cells. Interestingly, NKG2A+ PD-1+ CD8 T-cells expressed higher levels of both Perforin and Granzyme B, suggesting that these cells are cytotoxically potent. We found a similar upregulation of NKG2A in the NK cell population. NK cells from the primary tumor, but not the blood of HNSCC patients, significantly increased expression of inhibitory KIR2DL4, PD-1 and NKG2A. In addition, we determined that the ligand for NKG2A, HLA-E, was abundantly expressed on CD45+ monocytes and T-cells, but was absent on CD45- cells in the tumor. Finally, using the murine melanoma tumor model B16, we found that blocking NKG2A with monoclonal antibodies in conjunction with intratumoral STING injections resulted in significant immune mediated tumor rejection. Conclusions: We believe that this study provides the first characterization of human tumor-infiltrating NKG2A+ PD-1+ CD8 T-cells. We have shown that NKG2A+ CD8 T-cells express the highest levels of cytotoxic markers, suggesting an enhanced capacity to kill tumor cells, yet also the highest levels of checkpoint molecule expression. We have also shown that NKG2A is upregulated in tumor-infiltrating NK cells. Furthermore, we have demonstrated that blocking NKG2A in in vivo mouse models results in tumor rejection. Taken together, we believe this makes NKG2A an ideal therapeutic target to improve antitumor cytotoxic responses. Citation Format: Michael J. Korrer, Young Kim. The inhibitory checkpoint molecule NKG2A is upregulated on tumor-infiltrating NK cells and CD8 T-cells in human head and neck tumors [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A198.