Figure 2.

Antigen-specific cytotoxic T-lymphocytes and antigen-non-specific bystander T-cell killing in an immunogenic and suppressive tumor microenvironment. T-cells activated via TCR engagement up-regulate markers, including CD25, CTLA-4, and PD-1. Antigen-non-specific activated cytotoxic T-cells have a CD25⁻ and NKG2D⁺ phenotype. In the immunosuppressive environment antigen-non-specific activated T-cells may be resistant to suppressive signaling via PD-1 or CTLA-4 and may recognize targets expressing NKG2D ligands even when antigen is lost and MHC is down-regulated whereas antigen-specific T-cells may become anergic.