Figure 1.

Influence of co-regulatory immune checkpoint molecules on macrophage polarization in cancer. In various malignant diseases, the expression of such co-receptors is proven to alter tumor-associated macrophages towards the so-called M2 immune profile with reduced inflammation and thereby mostly “pro-tumor” activity. In contrast, minor expression of immune checkpoints correlates with the M1 macrophage type, characterized by cytotoxic immune cell activity and improved phagocytic ability that results in significant disease clearance. Therefore, inhibition of immune checkpoint expression on macrophages is a highly promising treatment strategy in cancer pathologies. Regarding colorectal cancer, pancreatic cancer and glioblastoma, predominantly PD-1 and CD47 are of great relevance and offer promising targets for checkpoint inhibition. Though, due to the fact that macrophages in different diseases are characterized by expression of different immune checkpoints, the importance of individual therapeutic approaches is highlighted. TAM, tumor-associated macrophages; EMT, epithelial mesenchymal transition.