Fig. 3.

Blockade of CTLA-4 or PD-1 Signaling in Tumor Immunotherapy. Dendritic cells (DC) and naive T cells interact in the lymph node during the priming phase. The interaction between the TCR and the tumor-associated antigen shown in the context of MHC II constitutes the activation signals. The interaction between CD28 and B7 expressed on the surface of DC is one of the additional activation signals. The immune system attacks and eliminates tumor cells as a result of the effector phase, which takes place in the peripheral tissue. At this stage, PD-1 and PD-L1 inhibitory signals on T cells are suppressed, effectively activating T cells against the tumor antigen