Cancer Cell Small Molecule Secretome Induces the Immune Checkpoint NKG2A and Dysfunction of Human CD8+ T Cells

Abstract

PD-1 blockade has been approved for head and neck squamous cell carcinoma (HNSCC) patients. However, many HNSCC patients do not respond to this treatment, and other tumor microenvironmental (TME) factors may promote resistance to PD-1 blockade. We previously identified increased expression of the inhibitory receptor NKG2A on CD8+ T cells in HNSCC tumors compared to T cells in matching PBMC samples. Mechanisms that promote NKG2A expression and the role of NKG2A on human T cells in the TME, however, are uncertain. We hypothesize that cancer cells can induce the expression of NKG2A and promote a dysfunctional phenotype on CD8+ T cells. Here we show that tumor-conditioned media (TCM) of HNSCC cancer cell lines or malignant ascites is sufficient to induce the expression of NKG2A and other inhibitory receptors on activated CD8+ T cells isolated from PBMCs of healthy donors. Boiling or small molecular weight cut-off filtering did not eliminate the effect of TCM, suggesting a small molecule promotes NKG2A. T cell activation in TCM decreased mitochondrial respiration to metabolically restrain CD8+ T cells. Functionally, T cell activation in TCM reduced CD8+ T cell cytotoxicity as shown by lower production of cytokines, granzyme B, and perforin. Furthermore, TCM prevented CD8+ T cells from killing cancer cells in response to a bispecific T cell engager. Thus, a secreted small molecule from HNSCC cancer cells can induce NKG2A expression and promote T cell dysfunction. Our findings may lead to targets for novel cancer therapies or biomarkers for NKG2A blockade response and provide a model to study T cell dysfunction and impaired metabolism.