T cell activation by antigen presentation. Tumour antigen presentation to T cell by dendritic cells (DC, on the left) is schematically depicted in this picture. The antigenic peptide complexed to the MHC, as indicated within the DC on the left, is recognised by the TCR on the T cell surface, as indicated within the T cell on the right. To effectively activate TAA-specific T cells, strong costimulation is needed. Costimulation depends on the integration between activatory (positive, as indicated on top of the MHC-TCR interaction) and inhibitory (negative, as indicated below the MHC-TCR interaction) bindings between ligands on the DC cell with their corresponding receptors on the T cell. For effective T cell activation and acquisition of effector activities, a third signal is necessary, provided by cytokines present in the immunological synapse, as indicated on top.