Figure 1. Tumour cells present antigens to T-cells as peptide fragments on the surface of major histocompatibility complex (MHC) molecules. (A) In the absence of co-stimulatory signals, tolerance may result. (B) Tumour antigens are also taken up by antigen presenting cells (APCs), which can present peptide fragments to both CD4+ and CD8+ T-cells. CD4+ T-cells secrete cytokines, which further amplify the CD8+ T-cell response. Activated CD8+ cells become cytotoxic and are then able to lyse tumour cells.
