Figure 1: Mechanisms of response and resistance to immune modulatory therapies. [A] Professional antigen-presenting cells, dendritic cells (green) and macrophages (brown), engulf and process tumour cells and their products before migrating to lymph nodes. [B] Anti-CTLA-4 mAb enhance priming of Teff and Treg leading to their expansion. [C] The activity of tumour-reactive Teff is limited by the engagement of PD-1 with its ligands PD-L1 (black/ white) and PD-L2 (black/yellow) on tumour and myeloid cells respectively. [D] Tumour-associated macrophages are typically described as pro-tumour, promoting tumour progression and invasion. [E] Macrophage activity is, however, context dependent, in pre-clinical studies anti-CTLA-4 mAb act additionally in the tumour to deplete CTLA-4 expressing Treg by ADCC, it is unclear whether this activity is common to ipilimumab.