T cell activation is strictly controlled
Because T cells are so powerful, there is a complex mechanism in place ensuring that T cell activation and discharge of toxins is strictly confined to target cells. This involves the specific recognition of a tumor-associated peptide (1) in combination with a surface molecule on tumor cells called MHC class I (2) by a matching T cell receptor (3). In addition, a bridge by co-stimulatory molecules and their ligands (4) is required in order to facilitate the T cell mechanism.