CD8A and neoplasm: For instance, in a Diethylnitrosamine (DEN)-induced hepatocellular carcinoma model, CD8+ T cells are enriched in the non-tumor microenvironment, but not within the tumor microenvironment [56].NKG2D may also have a potentially negative regulatory role in controlling TOX expression and the expression of tumor-reactive CD8+ T cells within the tumor microenvironment.